Ppoo Also I find it a bit hard to believe this is a hardwarw issue and not an os glitch/graphene issue.
I believe the GrapheneOS project has estimated having more than 250,000 users. If some bad thing happens to 1% of hardware running GrapheneOS in a given year, that bad thing will happen to 2,500 users in the year, or 200 per month. So far the description sounds very much like a hardware problem.
The problem could be software! But if it were a software problem in GrapheneOS and it were due to a recent update and it were even vaguely common there would be at least 10 reports on this forum. Just take a look at how many people posted about the Revolut Finance issue, or the Bluetooth crashes from (I think?) last spring.
At present it's hard to tell whether what you're experiencing is a gradual hardware failure or a software problem. Unfortunately, the way to conclusively show it's a software problem would be to replace the software. Perhaps a factory reset might do it, or re-flashing GrapheneOS, or flashing the device back to Google's stock OS. If one of those steps permanently solves the problem (as opposed to solving it for a day or two) then it's plausible that the problem was due to a software issue.