I checked and it looks just like the reboots that stopped a month ago.
First Kernel-Power Event ID 41 (critical), then after about 20 seconds WHEA-Logger Event ID 20.
Same stuff. Just funny why disabling fast boot kept this at bay for one month and then it started again.
But as I said I will have to wait for a few more days to see if the problem really has come back.
I wonder if a recent Windows update botched the thing again...