You are not the only one Siloi
I've started to have those issues as well, maybe for a couple of weeks/month or so. They are not that often and I've found no connection to anything I do or don't do whatsoever, they seem to be happening somewhat infrequently and at random times. Sometimes once every day or so, but now I've not seen it again for days. Who knows? Anyways it has been over 10 times, I've disabled auto-reboot and was/am using the phone everyday so it can't be that either. I'm on a Pixel 6a btw. I was also wondering might it be a hardware failure but now I'm not so sure..
Maybe there's something to investigate from GrapheneOS side of things?