Quick & Dirty Testing

Okay, so.I did a full TWRP backup, flashed the 16.0 build for my H990DS, the openGAPPS AROMA zip for 9.0 (importing all the same options I did when first installing 15.1) and the latest Magisk beta 17.3, following the installation instructions to the letter.This was a "DIRTY" flash over 15.1 (it's not really dirty when doing it how Lineage does its patching but I digress).No custom kernel, no Xposed (after flashing the xposed uninstaller). Just the ROM, GAPPS, Magisk and everything my phone already had on it.I previously had Gamma kernel, Xposed & Magisk.The device boots (takes about 10 mins the first time) and gets to the lock screen, and after a few seconds it shows "shutting down" when I'm in the middle of entering my PIN, turns off and boots back into recovery.I flashed the Magisk uninstaller, rebooted and tried again with the same result. I can see on the second screen for a few seconds that WiFi/Cell and Bluetooth are all working, and my watch pops up that it's connected to my V20 before it shuts off.I'm not willing to completely wipe and test in case something gets wiped that a TWRP backup has missed. Going to try to pull any logs I can and upload them.Edit: After a few more attemps including a battery pull, it booted and is currently in the system updating apps.Edit 2: Just did it again while I was taking screenshots. Was in the system for maybe 3-4 minutes. Going to try to install Magisk and get root for logs.Edit 2.5: Formatted /system and flashed the ROM clean, same issueEdit 3: @ x86cpu I managed to get a couple straight "adb shell dmesg" in between the device booting to the lock-screen and the shut-down occuring. I also got a kmsg from TWRP in case it's of any use. There's a lot of failures for stuff to opening and in the dmesg logs you can see where the shutdown occurs so maybe you'll be able to tell what's causing it.Logs are here and I'm going to revert to my 15.1 setup backup for now.I hope this helps! Do let me know if you need me to do the process again and manually pull any specific log files using TWRP.