It's not happening, when you have installed lineage's boot image? Can you reproduce it and get logcat for me? Maybe we can fix it.
The first file shows the classic crash after unlocking the device. The black lines showed up like last time.
The second one was surprising.
After it crashed and rebooted itself, I unlocked it and it… DIDN'T REBOOT! For whatever reason it was “working smoothly” UI felt a lot smoother, so then I opened youtube, but the app kept crashing. A few times it was stable enough to play a video, but then it eventually crashed, and then I just left it on the home screen, and it was smooth, but then the whole thing crashed and rebooted like normal. Unfortunately, I didn't catch if the black lines showed up this time. Then I just restored the boot.img with twrp and went back to the stock image.
Hope this is useful.
Also, there is this weird thing with MTP.
I have to press File transfer then press midi for it to show up on my Windows 10 pc.
If I just press File transfer then windows just give me a “cannot recognize device” / “device malfunction” error.
Just something weird. If I do the midi thing I can transfer files to it.
And this might not be very important, but I have had it repaired by some random repair shop. It didn't charge, so I think they just replaced the USB port. And when it ran the RR rom there were 2 times when it froze, probably cause of overheating, the screen was stuck on the last frame it displayed and made the classic BSOD sound until it ran out of battery.
Edit: Unlike last time, this time the tablet was fully loaded up with everything and had 3 user profiles.
*Logcat removed*