Same issue. Every two days I'm presented with a rebooted iMac in the morning. 1 external drive for Time Machine and a Fujitsu IX500 scanner attached. This has been happening under Big Sur for many months.

Same issue. Does this mean the sensor is bad? I tried unpairing and setting it up from scratch - that didn’t work. I tried a full reset- that didn’t work either to restore the blood oxygen app.