First, I use a mean well S-100F-12 (12 Volt 8.5 A)
This one I had some time and I wasn't using it.
I power the NanoPi true the 4-pin connector on the sata hat with a connector used from an old PC power supply. (All 4 wires connected)
I had some spare time this week-end and did some test with my NanoPi.
The problem seems to be more noticeable when I use midnight commander and copy files from usb to the sata hat.
It also shows up when copying files from network to sata true a samba share on the NanoPi.
Slowing down the CPU to 1800 ,1600 and 1400 did not make a difference.
Temperature found with htop was approx. 42-40°C at max CPU and at 1600 - 1400 about 36°C
I have a large slow turning fan on the NanoPi and a 50mm direct above the sata hat.
What I found strange is, that when I started from a cooled down NanoPi the NanoPi worked longer before failing than when is just rebooted and started again. (Or it is my imagination :-))
After another tip on https://forum.openmediavault.org/index.php/Thread/30512-Nanopi-crashes-on-file-transfers/ I restarted and used kernel 4.4.
The CPU is now running at 1800 with a temp of 30 a 35°C and I don’t seem to have this problem anymore.
At this point I'm not sure it's a power problem or a temperature problem but I'm planning to spend some more time on it this weekend.
There is also still a possibility that I received a faulty NanoPi or hat . . .