BlueSialia

So the root of the issue was obvious and so was the solution as well.
 
The docker and libvirt images where precisely in the disk with the least free space. Literaly less than 1 MB. Moving a couple files from that disk to another fixed everything. I was a little bit afraid of doing that while the data recovery was taking place, but everything went well from what I can tell.

I finally found a solution. But a very undesirable one. The issue was this. My Ryzen CPU doesn't support Unraid's (Linux) c-states. I disabled them in the BIOS. Now, as it is expected, my server has a very high power consumption even at idle.