Correct, it was running latest stock MM 6.0.1 before unlocking/rooting. I tried the official TWRP image (i think its 3.4 or 3.0.4) as well as the twrp that is provided by that guide during the second to last step. Definitely don't think it is twrp related. Of course all best practices of wiping data between flashes etc were used. I like to think I am a pretty advanced user.
When booting into download mode, it correctly says I am in developer mode or whatever because of the CID change.
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here are some logs after booting lineageos that I took thru adb while the device was on but the screen was black: https://pastebin.com/7yhL7FzM
looks like mostly errors about fingerprint sensor, radio drivers, some stuff about thermals, and camera drivers.