LG V20 H910 No Mobile Data, Calling & Kernel crash [4G, notifications solved] + Headphones not working

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Xanvast

Member
Jul 2, 2022
38
4
France
Hi, I have to say I didn't expect that this would be such a ride when I got into this. I am now simply trying to have a working phone again.

I will briefly sum up what I've done so far :

So I got a brand new V20 a few weeks ago with the intention to root it and install a custom rom. It came as a H91010l with a security patch from dec 2016.
I got everything ready it took a while but then went ahead and followed this guide [LS997|VS995|H910|F800L] DirtySanta Bootloader unlock and Root guide by me2151
A few minor hicups on the way but I got the bootloader unlocked, twrp installed and then LOS 18.1. I thought everything would be fine and I didn't make a backup... It worked well except that I had no mobile data (French carrier SFR), only sms worked and also some notification issues.

After a break and looking for solutions I tried another OS tonight (/e/) and the same issues were present. No mobile network.
It's not to do with the APN (which I made sure was configured properly) but likely some incompatibility after tweaking the system with the root procedure. Maybe something to do with US996 files being used.

So I decide that I needed to go back to stock since I wouldn't find a solution from there and I did a wipe before flashing a stock US996 firmware in TWRP taken in this thread, the US99610f - SPL 2016-12-01
Result : I lost the fast boot and TWRP, the phone is stuck on the LG logo.
Only one thing works at this point, firmware update download mode, so I did a full partition dl flash of the following H91510e_00_VTR_CA_OP_1205 kdz which according to many posts should be fine. Nope, it doesn't boot it's stuck on the LG logo.
I have tried a second one that is old, US99610f_00_1205 kdz which should work too. It boots and I get into setup but it reboots within a minute/30s on top of being really slow.

So what I'm looking for right now is a solution to go back to stock. I have no backup and no root. I can only use LGUP. And it seems that my model is pretty non cooperative. What can I do ?

Thank you.
 

Xanvast

Member
Jul 2, 2022
38
4
France
I was going to follow the instructions in this post and install the F800K10e.kdz but the lg-firmwares.com website is limiting me to 2 files per 24h so I decided to give the H91510e_00_VTR_CA_OP_1205.kdz another go. It wouldn't boot again until I formatted the data, it seems to be working so far.
I'm sure this is some noobie knowledge but most posts/guides didn't say to do that and I am indeed a beginner. I will update this thread with information on what I do next if relevant and if I can get my mobile data working somehow.

Edit : SMS work, 4G works but the sim card crashes when I call or get called.
Unfortunately I didn't even try my sim card when I got the phone so maybe it was the same onthe H91010l. Looks like I'll have to redo the unlocking procedure and continue fixing this mess.
Edit 2 : Notifications don't work properly either like on the custom roms... For example skype messages.
 
Last edited:

Darnrain1

Senior Member
Jan 2, 2018
471
134
USA
Hi, I have to say I didn't expect that this would be such a ride when I got into this. I am now simply trying to have a working phone again.

I will briefly sum up what I've done so far :

So I got a brand new V20 a few weeks ago with the intention to root it and install a custom rom. It came as a H91010l with a security patch from dec 2016.
I got everything ready it took a while but then went ahead and followed this guide [LS997|VS995|H910|F800L] DirtySanta Bootloader unlock and Root guide by me2151
A few minor hicups on the way but I got the bootloader unlocked, twrp installed and then LOS 18.1. I thought everything would be fine and I didn't make a backup... It worked well except that I had no mobile data (French carrier SFR), only sms worked and also some notification issues.

After a break and looking for solutions I tried another OS tonight (/e/) and the same issues were present. No mobile network.
It's not to do with the APN (which I made sure was configured properly) but likely some incompatibility after tweaking the system with the root procedure. Maybe something to do with US996 files being used.

So I decide that I needed to go back to stock since I wouldn't find a solution from there and I did a wipe before flashing a stock US996 firmware in TWRP taken in this thread, the US99610f - SPL 2016-12-01
Result : I lost the fast boot and TWRP, the phone is stuck on the LG logo.
Only one thing works at this point, firmware update download mode, so I did a full partition dl flash of the following H91510e_00_VTR_CA_OP_1205 kdz which according to many posts should be fine. Nope, it doesn't boot it's stuck on the LG logo.
I have tried a second one that is old, US99610f_00_1205 kdz which should work too. It boots and I get into setup but it reboots within a minute/30s on top of being really slow.

So what I'm looking for right now is a solution to go back to stock. I have no backup and no root. I can only use LGUP. And it seems that my model is pretty non cooperative. What can I do ?

Thank you.
If you did not make a dump backup there is not much you can do that I know of. You can try and delete the modemst1 and modemst2 and see if that fixes your no signal issue.

hold vol down plug phone into computer USB cable.

fastboot erase modemst1
fastboot erase modemst2
fastboot reboot

restart phone into os see if that fixes the issue.

If so make a backup of you EFS in twrp and save it.

Your EFS got corrupted when you flashed the stock KDZ to root the H910 happen to me also. This would explain why your phone is crashing and no signal.
 
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Xanvast

Member
Jul 2, 2022
38
4
France
If you did not make a dump backup there is not much you can do that I know of. You can try and delete the modemst1 and modemst2 and see if that fixes your no signal issue.

hold vol down plug phone into computer USB cable.

fastboot erase modemst1
fastboot erase modemst2
fastboot reboot

restart phone into os see if that fixes the issue.

If so make a backup of you EFS in twrp and save it.

Your EFS got corrupted when you flashed the stock KDZ to root the H910 happen to me also. This would explain why your phone is crashing and no signal.

I didn't flash any kdz to root initially. I just started flashing stuff once I lost my bootloader and TWRP. I managed to have the H91510e working that's where I'm at currently as per the second post. I will try and root it again following this procedure soon. I have to look into why I can't call or get called first. We'll see what happens, but according to this thread I will lose mobile network when I root the H915 version. I'll see when I get there.
 

Darnrain1

Senior Member
Jan 2, 2018
471
134
USA
Hi, I have to say I didn't expect that this would be such a ride when I got into this. I am now simply trying to have a working phone again.

I will briefly sum up what I've done so far :

So I got a brand new V20 a few weeks ago with the intention to root it and install a custom rom. It came as a H91010l with a security patch from dec 2016.
I got everything ready it took a while but then went ahead and followed this guide [LS997|VS995|H910|F800L] DirtySanta Bootloader unlock and Root guide by me2151
A few minor hicups on the way but I got the bootloader unlocked, twrp installed and then LOS 18.1. I thought everything would be fine and I didn't make a backup... It worked well except that I had no mobile data (French carrier SFR), only sms worked and also some notification issues.

After a break and looking for solutions I tried another OS tonight (/e/) and the same issues were present. No mobile network.
It's not to do with the APN (which I made sure was configured properly) but likely some incompatibility after tweaking the system with the root procedure. Maybe something to do with US996 files being used.

So I decide that I needed to go back to stock since I wouldn't find a solution from there and I did a wipe before flashing a stock US996 firmware in TWRP taken in this thread, the US99610f - SPL 2016-12-01
Result : I lost the fast boot and TWRP, the phone is stuck on the LG logo.
Only one thing works at this point, firmware update download mode, so I did a full partition dl flash of the following H91510e_00_VTR_CA_OP_1205 kdz which according to many posts should be fine. Nope, it doesn't boot it's stuck on the LG logo.
I have tried a second one that is old, US99610f_00_1205 kdz which should work too. It boots and I get into setup but it reboots within a minute/30s on top of being really slow.

So what I'm looking for right now is a solution to go back to stock. I have no backup and no root. I can only use LGUP. And it seems that my model is pretty non cooperative. What can I do ?

Thank you.
I know what's wrong. You cant use lineageos to make calls on AT&T network. You can get internet but no VoLTE. So your going to have to use a deblaoted Stock Oreo rom if you want a rooted phone with phone calls.

Custom Stock Oreo Rom Debloated & DeGoogled for the H910 & Most Lgv20 phones. VoLTE and WiFi-Calling working.
 
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Xanvast

Member
Jul 2, 2022
38
4
France
I know what's wrong. You cant use lineageos to make calls on AT&T network. You can get internet but no VoLTE. So your going to have to use a deblaoted Stock Oreo rom if you want a rooted phone with phone calls.

Custom Stock Oreo Rom Debloated & DeGoogled for the H910 & Most Lgv20 phones. VoLTE and WiFi-Calling working.
Thanks for your reply. I am using SFR, a French carrier. Is it the same issue ?
There has been developments since my last post. I started from the H91510e like I said and followed the [ROOT] HOWTO: AT&T H910 up to v20g (FULLY TESTED) guide by runningnak3d supported by a video from NewTechBegins. It went well until the flashing from TWRP.

I think it was my mistake to do like the video and flash h910-10r.rar followed by Magisk-v19.0. This resulted in not being able to boot, I kept getting the secure boot with password even after formatting. And after a couple of times it turned into a green screen crash. I couldn't get to recovery either for some reason even though I'm sure it was still there. The corruption warning message would appear almost instantly at boot and not allow me to do the volume down + power shortcut, and fastboot reboot recovery would not work either.

Reflashing the H91510e with LGUP worked but the system was particularly slow at first, it seemed to do better after a few minutes. Going over everything again, the part where we boot into recovery for the first time ended up the same with a green screen crash.

What seems to have solved it is to flash boot1.img from the root package in this [LS997|VS995|H910|F800L] DirtySanta Bootloader unlock and Root guide by me2151, which is different from the boot without extension of the other guide. I also reflashed the recovery several times, it didn't change anything until this.

I will continue updating this thread with the results of what follows next. I just have to install the h91010r now and manage to get to setup.

Edit : I just installed the h91010r with having wiped + formatted before and formatted after, it still goes into secure boot...
 
Last edited:

Darnrain1

Senior Member
Jan 2, 2018
471
134
USA
Thanks for your reply. I am using SFR, a French carrier. Is it the same issue ?
There has been developments since my last post. I started from the H91510e like I said and followed the [ROOT] HOWTO: AT&T H910 up to v20g (FULLY TESTED) guide by runningnak3d supported by a video from NewTechBegins. It went well until the flashing from TWRP.

I think it was my mistake to do like the video and flash h910-10r.rar followed by Magisk-v19.0. This resulted in not being able to boot, I kept getting the secure boot with password even after formatting. And after a couple of times it turned into a green screen crash. I couldn't get to recovery either for some reason even though I'm sure it was still there. The corruption warning message would appear almost instantly at boot and not allow me to do the volume down + power shortcut, and fastboot reboot recovery would not work either.

Reflashing the H91510e with LGUP worked but the system was particularly slow at first, it seemed to do better after a few minutes. Going over everything again, the part where we boot into recovery for the first time ended up the same with a green screen crash.

What seems to have solved it is to flash boot1.img from the root package in this [LS997|VS995|H910|F800L] DirtySanta Bootloader unlock and Root guide by me2151, which is different from the boot without extension of the other guide. I also reflashed the recovery several times, it didn't change anything until this.

I will continue updating this thread with the results of what follows next. I just have to install the h91010r now and manage to get to setup.
I would flash Auto_Debloat you get Oreo Debloat rom.
Custom Stock Oreo Rom Debloated & DeGoogled for the H910 & Most Lgv20 phones. VoLTE and WiFi-Calling working.

But to answer your question a lot of cell carriers are going to VoLTE only and LOS does not have that on the H910.

I made Auto_Debloat so if you need help just let me know.
 
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Xanvast

Member
Jul 2, 2022
38
4
France
I would flash Auto_Debloat you get Oreo Debloat rom.
Custom Stock Oreo Rom Debloated & DeGoogled for the H910 & Most Lgv20 phones. VoLTE and WiFi-Calling working.

But to answer your question a lot of cell carriers are going to VoLTE only and LOS does not have that on the H910.

I made Auto_Debloat so if you need help just let me know.
I added an edit at the bottom of my post, it displays the warning really quick and goes into secure boot everytime. Could it be that the h910-10r.rar package you shared at the end of the thread is not identical to the original post ? It simply won't boot into setup for me. Any ideas ?
I will try installing something quick tonight to have a working system with recovery I'm done messing around for the day. I will look into your custom rom in the coming days thanks for your help !
 

Darnrain1

Senior Member
Jan 2, 2018
471
134
USA
I added an edit at the bottom of my post, it displays the warning really quick and goes into secure boot everytime. Could it be that the h910-10r.rar package you shared at the end of the thread is not identical to the original post ? It simply won't boot into setup for me. Any ideas ?
I will try installing something quick tonight to have a working system with recovery I'm done messing around for the day. I will look into your custom rom in the coming days thanks for your help !
Yes your data partition is encrypted still. You need to format it in twrp.
 

Xanvast

Member
Jul 2, 2022
38
4
France
Yes your data partition is encrypted still. You need to format it in twrp.
That's the thing, it still goes into secure boot after formatting it.
So I flashed the boot1 again and twrp to be safe, it now doesn't display the warning anymore but goes into the green screen crash after a minute or so.
I'm now back to twrp, I'll just wipe everything and install LOS to try. If at least it has mobile data that would be more than before.
 

Darnrain1

Senior Member
Jan 2, 2018
471
134
USA
That's the thing, it still goes into secure boot after formatting it.
So I flashed the boot1 again and twrp to be safe, it now doesn't display the warning anymore but goes into the green screen crash after a minute or so.
I'm now back to twrp, I'll just wipe everything and install LOS to try. If at least it has mobile data that would be more than before.
Yes you need a kernel. Your still running stock kernel that's why your getting the green screen. :)
 
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Xanvast

Member
Jul 2, 2022
38
4
France
Yes you need a kernel. Your still running stock kernel that's why your getting the green screen. :)
Oh I see now, so it's indeed not the same package. That is why you had to flash H910_BTTF-mk2000.zip
Thanks for your time and patience.
I installed LOS 18.1 and it works fine with 4G this time (before reading your reply). Unsurprisingly calls in and out make the phone kernel crash with a black screen. I really like LOS and android 11, is there something I can do to make calls work ? Like flashing another kernel ? Does /e/OS have the same issue ?
If not I can absolutely live without calls for the moment, no problem.

Edit : I'm not getting notified of messages for Discord/Skype and not getting the call if the app is not open actively. Seems like it's not running the services in the background.
 
Last edited:

Darnrain1

Senior Member
Jan 2, 2018
471
134
USA
That's the thing, it still goes into secure boot after formatting it.
So I flashed the boot1 again and twrp to be safe, it now doesn't display the warning anymore but goes into the green screen crash after a minute or so.
I'm now back to twrp, I'll just wipe everything and install LOS to try. If at least it has mobile data that would be more than before.
It's complicated,
Oh I see now, so it's indeed not the same package. That is why you had to flash H910_BTTF-mk2000.zip
Thanks for your time and patience.
I installed LOS 18.1 and it works fine with 4G this time (before reading your reply). Unsurprisingly calls in and out make the phone kernel crash with a black screen. I really like LOS and android 11, is there something I can do to make calls work ? Like flashing another kernel ? Does /e/OS have the same issue ?
If not I can absolutely live without calls for the moment, no problem.
Yep your welcome, no problem. You may just need to setup LOS with your network provider. Do a google search for APN carrier settings for your cell provider. Take care.
 

Xanvast

Member
Jul 2, 2022
38
4
France
It's complicated,

Yep your welcome, no problem. You may just need to setup LOS with your network provider. Do a google search for APN carrier settings for your cell provider. Take care.
That's the first thing I've done, I entered the APN settings from this page (3), and the results reported are from after. So do you know about other OS like /e/, any that would not behave the same ? Or anything I can flash on top to fix it ?
Have a good evening.
 

Darnrain1

Senior Member
Jan 2, 2018
471
134
USA
That's the first thing I've done, I entered the APN settings from this page (3), and the results reported are from after. So do you know about other OS like /e/, any that would not behave the same ? Or anything I can flash on top to fix it ?
Have a good evening.
I am in the USA so it's in the afternoon for me.

You may want to try and flash you EFS from fastboot mode.

Manually reinstall your EFS on the Lgv20.

You need to find your Original DUMP of the rom your Lgv20 phone was on, before you downgraded your firmware for rooting.
Note: COM21 is what ever com port you were using at the time.
Reboot into fastboot mode
With the phone powered off hold the down vol and plug in usb to computer.

Info on what the files are

/fsg

A backup of your modemst1 and modemst2 files. So if you erase modemst1 and modemst2 /fsg should restore the partitions automatically. But if /fsg is corrupted then it will not restore them.

/misc
This partition contains miscellaneous system settings.

/modemst1 /modemst2
Modemst1 and modemst2 store information like IMEI.


fastboot flash fsg fsg_COM21
fastboot flash misc misc_COM21
fastboot flash modemst1 modemst1_COM21
fastboot flash modemst2 modemst2_COM21
fastboot reboot
 
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Xanvast

Member
Jul 2, 2022
38
4
France
I am in the USA so it's in the afternoon for me.

You may want to try and flash you EFS from fastboot mode.

Manually reinstall your EFS on the Lgv20.

You need to find your Original DUMP of the rom your Lgv20 phone was on, before you downgraded your firmware for rooting.
Note: COM21 is what ever com port you were using at the time.
Reboot into fastboot mode
With the phone powered off hold the down vol and plug in usb to computer.

Info on what the files are

/fsg
A backup of your modemst1 and modemst2 files. So if you erase modemst1 and modemst2 /fsg should restore the partitions automatically. But if /fsg is corrupted then it will not restore them.

/misc
This partition contains miscellaneous system settings.

/modemst1 /modemst2
Modemst1 and modemst2 store information like IMEI.


fastboot flash fsg fsg_COM21
fastboot flash misc misc_COM21
fastboot flash modemst1 modemst1_COM21
fastboot flash modemst2 modemst2_COM21
fastboot reboot
Unfortunately as stated in my first post, I have no backup of the state of the phone when I got it as a H91010l. I didn't do one either while on the H91510e because I didn't see the point, it was already modified and calling didn't work.
Thank you for the explanation.

Something I'd like to mention for other readers is that there is one main visible difference between the first root (from H91010l with the old guide) and second one (H91510e with newer guide). The first time the warning message with the red triangle during boot was very distorted and duplicated. It was unreadable. Now it is clear. I don't know enough to say what was causing it or point at what made 4G work in the second case but this was something worth noting.
 
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Xanvast

Member
Jul 2, 2022
38
4
France
Alright, going into this de-Googling trip I did not know that many apps relied on Google Play Services to work and the Google cloud services, Firebase cloud etc... to send their notifications. I had no idea that Google was managing the notifications for most of the world and so much more. That only reinforces my desire to get away from it.

So these apps like Discord, Skype and others that don't send notifications it's directly because of the lack of Google Play Services. I noticed today that MicroG has a Cloud Messaging option but I will not enable it.
Signal works fine without any of it. I also found Skype Lite to send notifications so that's what I'll use from now on. Discord is going into the trash. I've read that Telegram is supposed to work too. So another problem solved. I have no issues making concessions on my convenience to be freer.
A website I came across which references how apps behave without Google : https://plexus.techlore.tech/
 

Xanvast

Member
Jul 2, 2022
38
4
France
It's complicated,
Oh I see now, so it's indeed not the same package. That is why you had to flash H910_BTTF-mk2000.zip
Thanks for your time and patience.
I installed LOS 18.1 and it works fine with 4G this time (before reading your reply). Unsurprisingly calls in and out make the phone kernel crash with a black screen. I really like LOS and android 11, is there something I can do to make calls work ? Like flashing another kernel ? Does /e/OS have the same issue ?
If not I can absolutely live without calls for the moment, no problem.

Edit : I'm not getting notified of messages for Discord/Skype and not getting the call if the app is not open actively. Seems like it's not running the services in the background.
Yep your welcome, no problem. You may just need to setup LOS with your network provider. Do a google search for APN carrier settings for your cell provider. Take care.

I took photos of my Kernel crashes, now it doesn't just happen with calls, which I could live with but also while using Skype Lite and looking out of the app for example, when I'm doing something taxing for the device or sometimes the phone would just reboot. Several times a day.
It seems to be very similar to what is mentioned in this post. Do you or anybody think that I should do the same and flash h915freedommobilemodem.img ? How do I go about it if so ? Is that something you do in fastboot ?
Also what are the risks if it goes bad ? I'm tired of dealing with repairing the mess and I'd like to avoid more problems.
Thanks.
 

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Darnrain1

Senior Member
Jan 2, 2018
471
134
USA
I took photos of my Kernel crashes, now it doesn't just happen with calls, which I could live with but also while using Skype Lite and looking out of the app for example, when I'm doing something taxing for the device or sometimes the phone would just reboot. Several times a day.
It seems to be very similar to what is mentioned in this post. Do you or anybody think that I should do the same and flash h915freedommobilemodem.img ? How do I go about it if so ? Is that something you do in fastboot ?
Also what are the risks if it goes bad ? I'm tired of dealing with repairing the mess and I'd like to avoid more problems.
Thanks.
If I am not mistaken your running LineageOS. I would ask in that post for help. I run Stock Oreo on my H910 because everything works.

[OFFICIAL] LineageOS 18.1 for the LG V20
 

Xanvast

Member
Jul 2, 2022
38
4
France
If I am not mistaken your running LineageOS. I would ask in that post for help. I run Stock Oreo on my H910 because everything works.

[OFFICIAL] LineageOS 18.1 for the LG V20
Yes the post is in that thread. I didn't have this problem the first time I used LOS 3 weeks ago so I assume it has to do with the green screen crash caused by the kernel I didn't flash after the h910-10r.rar. So it's still unaddressed in my opinion. Should I go ahead and flash that missing kernel or the H915 modem ? I don't know what's the difference and both seem plausible.
It's fine if you aren't sure and I will end up asking there.
 
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    Hi, I have to say I didn't expect that this would be such a ride when I got into this. I am now simply trying to have a working phone again.

    I will briefly sum up what I've done so far :

    So I got a brand new V20 a few weeks ago with the intention to root it and install a custom rom. It came as a H91010l with a security patch from dec 2016.
    I got everything ready it took a while but then went ahead and followed this guide [LS997|VS995|H910|F800L] DirtySanta Bootloader unlock and Root guide by me2151
    A few minor hicups on the way but I got the bootloader unlocked, twrp installed and then LOS 18.1. I thought everything would be fine and I didn't make a backup... It worked well except that I had no mobile data (French carrier SFR), only sms worked and also some notification issues.

    After a break and looking for solutions I tried another OS tonight (/e/) and the same issues were present. No mobile network.
    It's not to do with the APN (which I made sure was configured properly) but likely some incompatibility after tweaking the system with the root procedure. Maybe something to do with US996 files being used.

    So I decide that I needed to go back to stock since I wouldn't find a solution from there and I did a wipe before flashing a stock US996 firmware in TWRP taken in this thread, the US99610f - SPL 2016-12-01
    Result : I lost the fast boot and TWRP, the phone is stuck on the LG logo.
    Only one thing works at this point, firmware update download mode, so I did a full partition dl flash of the following H91510e_00_VTR_CA_OP_1205 kdz which according to many posts should be fine. Nope, it doesn't boot it's stuck on the LG logo.
    I have tried a second one that is old, US99610f_00_1205 kdz which should work too. It boots and I get into setup but it reboots within a minute/30s on top of being really slow.

    So what I'm looking for right now is a solution to go back to stock. I have no backup and no root. I can only use LGUP. And it seems that my model is pretty non cooperative. What can I do ?

    Thank you.
    If you did not make a dump backup there is not much you can do that I know of. You can try and delete the modemst1 and modemst2 and see if that fixes your no signal issue.

    hold vol down plug phone into computer USB cable.

    fastboot erase modemst1
    fastboot erase modemst2
    fastboot reboot

    restart phone into os see if that fixes the issue.

    If so make a backup of you EFS in twrp and save it.

    Your EFS got corrupted when you flashed the stock KDZ to root the H910 happen to me also. This would explain why your phone is crashing and no signal.
    1
    Hi, I have to say I didn't expect that this would be such a ride when I got into this. I am now simply trying to have a working phone again.

    I will briefly sum up what I've done so far :

    So I got a brand new V20 a few weeks ago with the intention to root it and install a custom rom. It came as a H91010l with a security patch from dec 2016.
    I got everything ready it took a while but then went ahead and followed this guide [LS997|VS995|H910|F800L] DirtySanta Bootloader unlock and Root guide by me2151
    A few minor hicups on the way but I got the bootloader unlocked, twrp installed and then LOS 18.1. I thought everything would be fine and I didn't make a backup... It worked well except that I had no mobile data (French carrier SFR), only sms worked and also some notification issues.

    After a break and looking for solutions I tried another OS tonight (/e/) and the same issues were present. No mobile network.
    It's not to do with the APN (which I made sure was configured properly) but likely some incompatibility after tweaking the system with the root procedure. Maybe something to do with US996 files being used.

    So I decide that I needed to go back to stock since I wouldn't find a solution from there and I did a wipe before flashing a stock US996 firmware in TWRP taken in this thread, the US99610f - SPL 2016-12-01
    Result : I lost the fast boot and TWRP, the phone is stuck on the LG logo.
    Only one thing works at this point, firmware update download mode, so I did a full partition dl flash of the following H91510e_00_VTR_CA_OP_1205 kdz which according to many posts should be fine. Nope, it doesn't boot it's stuck on the LG logo.
    I have tried a second one that is old, US99610f_00_1205 kdz which should work too. It boots and I get into setup but it reboots within a minute/30s on top of being really slow.

    So what I'm looking for right now is a solution to go back to stock. I have no backup and no root. I can only use LGUP. And it seems that my model is pretty non cooperative. What can I do ?

    Thank you.
    I know what's wrong. You cant use lineageos to make calls on AT&T network. You can get internet but no VoLTE. So your going to have to use a deblaoted Stock Oreo rom if you want a rooted phone with phone calls.

    Custom Stock Oreo Rom Debloated & DeGoogled for the H910 & Most Lgv20 phones. VoLTE and WiFi-Calling working.
    1
    Thanks for your reply. I am using SFR, a French carrier. Is it the same issue ?
    There has been developments since my last post. I started from the H91510e like I said and followed the [ROOT] HOWTO: AT&T H910 up to v20g (FULLY TESTED) guide by runningnak3d supported by a video from NewTechBegins. It went well until the flashing from TWRP.

    I think it was my mistake to do like the video and flash h910-10r.rar followed by Magisk-v19.0. This resulted in not being able to boot, I kept getting the secure boot with password even after formatting. And after a couple of times it turned into a green screen crash. I couldn't get to recovery either for some reason even though I'm sure it was still there. The corruption warning message would appear almost instantly at boot and not allow me to do the volume down + power shortcut, and fastboot reboot recovery would not work either.

    Reflashing the H91510e with LGUP worked but the system was particularly slow at first, it seemed to do better after a few minutes. Going over everything again, the part where we boot into recovery for the first time ended up the same with a green screen crash.

    What seems to have solved it is to flash boot1.img from the root package in this [LS997|VS995|H910|F800L] DirtySanta Bootloader unlock and Root guide by me2151, which is different from the boot without extension of the other guide. I also reflashed the recovery several times, it didn't change anything until this.

    I will continue updating this thread with the results of what follows next. I just have to install the h91010r now and manage to get to setup.
    I would flash Auto_Debloat you get Oreo Debloat rom.
    Custom Stock Oreo Rom Debloated & DeGoogled for the H910 & Most Lgv20 phones. VoLTE and WiFi-Calling working.

    But to answer your question a lot of cell carriers are going to VoLTE only and LOS does not have that on the H910.

    I made Auto_Debloat so if you need help just let me know.
    1
    That's the thing, it still goes into secure boot after formatting it.
    So I flashed the boot1 again and twrp to be safe, it now doesn't display the warning anymore but goes into the green screen crash after a minute or so.
    I'm now back to twrp, I'll just wipe everything and install LOS to try. If at least it has mobile data that would be more than before.
    Yes you need a kernel. Your still running stock kernel that's why your getting the green screen. :)
    1
    That's the first thing I've done, I entered the APN settings from this page (3), and the results reported are from after. So do you know about other OS like /e/, any that would not behave the same ? Or anything I can flash on top to fix it ?
    Have a good evening.
    I am in the USA so it's in the afternoon for me.

    You may want to try and flash you EFS from fastboot mode.

    Manually reinstall your EFS on the Lgv20.

    You need to find your Original DUMP of the rom your Lgv20 phone was on, before you downgraded your firmware for rooting.
    Note: COM21 is what ever com port you were using at the time.
    Reboot into fastboot mode
    With the phone powered off hold the down vol and plug in usb to computer.

    Info on what the files are

    /fsg

    A backup of your modemst1 and modemst2 files. So if you erase modemst1 and modemst2 /fsg should restore the partitions automatically. But if /fsg is corrupted then it will not restore them.

    /misc
    This partition contains miscellaneous system settings.

    /modemst1 /modemst2
    Modemst1 and modemst2 store information like IMEI.


    fastboot flash fsg fsg_COM21
    fastboot flash misc misc_COM21
    fastboot flash modemst1 modemst1_COM21
    fastboot flash modemst2 modemst2_COM21
    fastboot reboot