Hey there,
I have a NanoPiM4v2 with the SATA-Hat and I'm powering it using a standard ATX PSU.
The NanoPi "turns off" after about 8-48 hours of uptime. When this happens, the "Heartbeat"-LED turns off, while all others stay normal.
The NanoPi doesn't actually power off however, as I need to long-press the power button to turn it off completely, before turning it on again.
I've tried checking the logs, but they all seem normal until they just cut off.