OK so lets do an overview of how to flash TOTs from now on. Steps below will allow you to flash ZV9 (or higher) and also downgrade back to ZV6. Don't flash ZV5 TOT if you're on ZV6 or higher! ZV5 is qfuse v1.. ZV6 and ZV9 are qfuse v2. You can only flash equal or higher qfuse versions... NEVER lower. I mean, technically you can flash ZV5... but you will not be able to boot the phone after doing so.
Thanks to some testing from @Awesomeslayerg
I think we've worked out all the kinks. I don't have a Sprint G4, so without him the specific details laid out below would not have come so quickly.
1. Download both LGUP msi files HERE
and install them on your PC.
2. Boot your phone into Download Mode [Remove USB cable in phone. Power off phone. Hold Volume Up then plug in USB cable]
3. Open LGUP, select your phone model. If it says unknown, disconnect phone/reopen LGUP and try again.
4. With LGUP now opened, select the "Upgrade" option. Then below that.. select the TOT you wish to flash then hit START.
5. That's it! Just wait for it to finish flashing. LGUP makes things quite simple. You don't even have to use COM port 41 any more. Always use the upgrade option.. even when downgrading.
If LGUP doesn't wipe your data and you'd prefer to have it wiped for some reason or another... simply boot into stock recovery after the TOT flash and run a factory reset.
If you have ignored the steps above and decided to use the old "LG Flash" method, forgot to check off "Board DL" and are now stuck on the "2" screen..
1. Use LGUP to flash ZV6 and get stuck at blue screen with red "2".
2. Power off phone and close LGUP.
3. Boot into Download Mode again.
4. This time.. instead of using LGUP.. use the original LG Flash method HERE
5. Make sure you set LG Flash to use "Board DL" at the bottom of the screen where u select DLL and TOT.
6. Should be able to flash either ZV6 or ZV9 using LG Flash (with Board DL option).