I wanted to ask if there has been any update on this?
I'm experiencing the same issues with my unraid server.
I just shuts off, syslog doesn't show anything (it just stops at some point), so it's not related to an error in unraid.
I've switched the PSU yesterday and I still have the same problem. Interestingly, the server always finishes the parity check and seems to experience a random shutdown when there is no load.
I'll recheck the hardware, try one ram stick at a time and then maybe the motherboard.