Do you have any hardware in your rig that isnt connect properly? like SSD or harddisk where you only connect the sata cable but nvr connect the power cable becos you try to isolate something earlier. I noticed random restart happens previously when I didnt connect my sata cable to my harddisk but there is power cable connect to it. After I connect everything the system stop random restart. maybe you can check if you did anything to your hardware recently. Things dont happen suddenly when it has been doing fine all along.