I installed the latest Big Sur update recently, I'm now running 11.2.1(20D74). This morning, when waking from sleep - on recharge, everything looked OK for a few seconds then before I could start to do anything, the entire screen flashed Magenta for a 10th of a second aprox, then rebooted as if from cold. No error signal, no start up chime. It's OK now, but I think it may have done this before while I was not looking as I have found that odd aspects of the system have reset, I'm really not clear on that at the moment though.