grapheneos_noob Can I ask You to Submit Your situation to the Official GrapheneOS Bug Reports? It will Greatly Help mу (and others in the future).
Broken hardware is not something to submit to software developers to fix. Based on the description so far, unfortunately your device is probably broken. The report from itsjpb is about a broken device that was fixed by a repair shop.
I believe the prudent things to do are:
- Flash your device back to the stock OS, use it long enough for it to exhibit the bad behavior, and take it to a repair shop (or mail it to Google), or
- Find a repair shop that is not alarmed by repairing a device running a non-Google OS.
I believe a qualified Pixel Tablet repair tech would quickly diagnose the device as broken after seeing it misbehave that way.