I just upgraded from 6.9 to 7.3.2 yesterday. I woke up to my server asleep and unresponsive, with the power button blinking (which I've never seen it do before). I pushed the button to power it back on and it was responsive within moments. After some investigation, it appears that the Sleep (s3) plugin is a default part of Unraid now (?) and has a default sleep schedule. Maybe check out this plugin.