Okay, more insights:
For the things dependent on the number of CPUs, I found a suspect:
I suspect this to be L9 or L10 from the schematics. I'll try to find someone who can help me replace that sucker. Before that, there's probably little sense in trying to resolve the other issue.
- The bookworm kernel 6.1.0-39 manages to enumerate the SATA card reliably if I limit the number of CPUs to 2.
- The trixie kernel 6.12-something reliably fails to boot with the SATA card in no matter the number of CPUs allowed.
- Without the SATA card, the trixie kernel boots cleanly with only two CPUs.
For the things dependent on the number of CPUs, I found a suspect:
I suspect this to be L9 or L10 from the schematics. I'll try to find someone who can help me replace that sucker. Before that, there's probably little sense in trying to resolve the other issue.

