[G3 Q&A, Help & Troubleshooting] Mugatu485:
Hey there,

I recently tried to upgrade to Nougat 7.1 by flashing Lineage 14.1 (latest Nightly) or Resurrection Remix 5.8.0 / 5.9.2 via TWRP 3.1.0-2. But somehow I can't get the system to work.

At first I went from Fulmics 6.9 to Lineage. TWRP -> Factory Reset -> Flash ROM -> Flash GAPPS 7.1 Pico -> [1st attempt Reset Cache + Dalvik] / [2nd attempt: Factory Reset] -> Reboot. Same procedure for RR 5.8.

After flashing the boot animation appears for a while and then, finally, the screen turns black, then reboot. When the screen is black I can still push the power button and hear the wakeon sound. But the screen is still empty. At some point I managed to get to the first step of system configuration (language selection) just by waiting one or two minutes. But on the next step the screen tuns black again and eventually freezes. Sometimes I can even see the status bar and change the volume bars for example, but the installation process somehow cannot initialize properly. Most of the time the system just turns black, freezes and then reboots sooner or later. I tried different builds of RR (5.8.0 of 2016 and 2017 as well as the newer 5.8.2) and Lineage (13.0 / 14.1) but the issue is always the same.

On my first attemps - coming from Fumlics 6.9 - I even had problems with the modem. But after switching between 30B and 21C flashing ROMs (7.1 in particular) went mostly fine.

In the meantime I have even performed a full reset via LGUP / LG Flash Tool 2014 to D85521C_00_1204.kdz, Android 5.0 LP with Baseband 13.2-00002 (modem 21c). After rooting with Kingroot, applying TWRP with AutoRec and upgrading to the latest version (3.1.0-2) I tried the whole thing again.

Flashing Nougat RR / Lineage, Gapps, then Factory Reset and Reboot. The issue is still the same... blackscreen, freeze, reboot. Also flashing MR_Bump.zip after the Nougat / Gapps makes no difference. When applying the .zip via TWRP, the system suddenly shuts down and reboots, then the same Nougat bootloop as mentioned before.

Interestingly it isn't even possible to flash back to Fulmics 6.6 after trying a 7.1 Nougat version. When flashing the system just shuts down, then reboots. The ROM won't install. Other MM ROMs have problems after trying to flash Nougat, as well. For most of them I get the same bootloop / freeze phenomenon.

So the only chance is to completely reset back to LP 5.0 via LGUP / Flash Tool 2014 again...

I am not really sure what is going wrong with the system. But generally speaking LP and upgrading to MM and its variants appears to work fine.

Only trying to flash Nougat leads to perpetual bootloops with any ROMs.

Is there any chance to make Nougat run on my D855?

Anything else I could try to fix the issues mentioned above?

Would be grateful for any help! :)

Edit:

After installing another 6.0 Marshmallow yesterday I oncemore tried flashing two other Nougat ROMs. The first one was AICP, the second crDroid. When flashing in TWRP I noticed that there was a basband incompatibility again. The ROMs required the 21c, which was already installed (by the lastest MM 6.0) but still marked as unsupported. After that I tried flashing Step-hans 21c in the first place and finally got the two ROMs to install. However, after the unconditional flashing procedure I always got two lines of an "Unknown Command [log]" error...

AICP just gave me the black screen after the boot animation again, but suprisingly crDoid booted without any issue. At least I could make it run normally for one or two minutes. Entering the menus, pushing buttons, opening apps just worked fine for that short period. And then the screen finally faded to black again. I could still use the power button and see the display powering on and off. But the screen itself was still black. Maybe my device has problems with running Nougats system UI...?