Help diagnosing server freeze issue

https://piefed.social/post/1158809

I had a similar issue on an HP Elitedesk 800 mini G3. It turned out to be a faulty ram stick. Memtest revealed the issue and after unpligging the defective stick the issue was resolved.
Memtest is the easiest and best place to start.
Thank you!!! I think this is the issue. With one of the ram sticks in I can memtest just fine. With the other it never finishes and it just reboots.

Definitely suspect.

You should be able to let memtest run for days with no problems, so a reboot would either be a faulty stick or possibly a faulty motherboard slot.

Swap the RAM between slots to isolate the root cause

Yeah I think you found it, my server had the same symptoms and a bad RAM stick was the cause.