OptiPlex 5070 SFF randomly rebooting on TrueNAS SCALE, logs show no errors

Hey guys,

I recently bought a refurbished Dell OptiPlex 5070 SFF running TrueNAS SCALE. It came with an i5-8500T and 8GB RAM, but I upgraded it to 32GB total (4×8GB DIMMs).

Storage setup:

- 2× 3.5" HDDs

- 1× 128GB SATA SSD

- 1× 512GB SSD for TrueNAS apps/data

The system works fine overall, but it randomly reboots without warning. Sometimes it runs for around 25 hours before rebooting, and other times it may take 1-2 days. It can even happen while the system is idle.

What makes this strange is that I don't see any kernel panics, freezes, or obvious errors in the logs before the reboot. The logs look clean, as if the system suddenly lost power or restarted unexpectedly.

Could this be caused by faulty RAM, PSU issues, motherboard problems, BIOS settings, overheating, or something else? Has anyone seen similar behavior with a refurbished OptiPlex 5070 SFF running TrueNAS SCALE?

Any suggestions on what diagnostics or logs I should check next would be appreciated.