It's been a long time since I've encountered this kind of obtuseness. This
is not new, but I thought that this kind of blindness was in the rear-view
mirror. I guess not.
One of their motherboards keeps locking up on me. After some back and forth
their last reply ended the discussion thread with a:
# Since we do not fully support and validate Linux, we cannot offer full
# support on Linux. Please try a Windows base OS to check if you are still
# experiencing the same instability issue.
As suggested, you should be able to do this without purchasing a license,
and it would give you a way to install firmware updates.
Just thought I'd mention it here, so that other DIYers might take this into
consideration. Looking at their support page, it's listing new BIOS updates
every month.
It would be worth searching for other reports of problems with the same
motherboard regardless of OS. Also look for details of the BIOS updates.
Modern hardware is pretty uniform, so the same problem often crops up
on other instances. Non-reproducible problems tend to be with cables
and connectors.
Try stripping down to the most basic configuration and swapping the remaining
add-ons (GPU, mass storage, cables).