Fingerprint not detecting in custom os since installed official 8.1

[hondraopranav]

Fingerprint not detecting since I have installed custom ROM after I have installed official Oreo
On official Oreo fingerprint shows up in settings but in custom Oreo all works fine and best but fingerprint doesn't show up in any settings I have tried 4 8.1 custom roms like sex pixelexpirience 64 bit versions all works flawlessly tested Google camera it works the best but not detecting fingerprint even after searching fingerprint it only shows up gestures's fingerprint in gestures's system menu PLZZ give me link of official Oreo build OPSS28.65-36-3 with Indian band so I could try to flash via fastboot and then recheck if custom roms fingerprint gets detected or not..

 

[Surya Guduru]

Update ur bootloader to Oreo one and then try flashing the rom

 

[hondraopranav]

Update ur bootloader to Oreo one and then try flashing the rom

I don't have fastboot official oreo link can anyone give me plzz

 

[Surya Guduru]

I don't have fastboot official oreo link can anyone give me plzz

U told u had the official 8.1 ROM ....in that ...... fastboot Flash bootloader bootloader.zip and fastboot flash modem non-hlos.bin

 

[Jorge Lucas]

change the base of your fp to nougat base again

 

[Coala990]

Hey check this out

 

[lufusol]

U told u had the official 8.1 ROM ....in that ...... fastboot Flash bootloader bootloader.zip and fastboot flash modem non-hlos.bin

The OP didn't say they had the official 8.1 ROM, they said they had installed official Oreo. AFAIK There is no official 8.1 ROM for Sanders. Some people have taken the OTA for their device and repackaged it into an UNofficial flashable package, but that's not the same thing, and reportedly may be causing problems on EU & US variants, so I wouldn't recommend it.

I have the same problem with my FP reader.
I don't have an official 8.1 ROM (because there isn't one, lol), but I installed stock nougat 7.1.1 (retus, in my case) and then got the OTA upgrade to 8.1, after that fp+VoLTE are 100% working.

Then, as soon as I change to a custom 8.1 (or 9) ROM, VoLTE still works, but the fp is no longer recognized by the system.

If I flash back to stock nougat, FP comes back (and LTE breaks, but can be fixed by installing the 8.1 OTA upgrade again, or by getting to a root terminal and fixing permissions on /persist, I've personally verified both methods to restore functionality (assuming your /persist is unmolested - if it is, you're SoL).

Going from fully working official nougat or official Oreo, to any Oreo (or Pie) custom ROM still seems to break the FP reader again. I'm getting really tired of wiping my device...

Not A Solution #1
As suggested here: With FP + VoLTE working under official 8.1 OTA update, I installed TWRP & backed up /EFS, then installed my custom 8.1 ROM (Validus final) and restored the backed up /EFS, but instead of bringing my FP back, it just caused bootloop and I had to roll back to stock and start over. I skipped rolling back to Nougat before flashing custom, is that important? Why would it matter?

Not A Solution #2
After installing the custom 8.1 ROM I tried flashing the Nougat FP base. It had no effect.

Maybe A Solution? UPDATE: YES. A SOLUTION.
As suggested in this post:

1 - download the latest nougat stock rom (link removed - the correct one will vary depending on your device, up to you to obtain the correct firmware);
2 - unzip the above file and cd into the resulting directory;
3 - reboot your phone in fastboot mode;
4 - from terminal (linux or windows, in linux I had to do it as root user, using sudo), type:
fastboot flash bootloader bootloader.img <enter>
fastboot flash modem NON-HLOS.bin <enter>
fastboot reboot <enter>

By doing above steps, your phone should get fingerprint options back.

I did this, it worked, with one additional step - I had a pattern set before. After the fingerprint reader was 'reinstated' the pattern no longer worked. Rebooting into Recovery and flashing lockfix.zip removed the security so that I could set it up again properly. Find lockfix.zip in this post.