GMKtec Nucbox G3 powering down unexectedly

[StevenFriedrich]

I bought the G3 to create a NAS, using an 8-bay USB drive bay.
I did a fresh install of debian12 and selected no Gnome, just Plasma desktop environment (with debian desktop too)
I set System Settings...Power Management...Activity Power Settings to Define a special behavior:
Never shut down the computer or let it go to sleep

Under Plasma, there is a sensor for the nvme drive, I don't know if it works on this nucbox g3/
The machine unexpectedly powers down.
I put a heatsink on the ssd (a Mason Semi 256GB shipped with)
The sensor didn't show temps above 50 degrees centigrade.

Any ideas?