Ok, running for approx. 4 days now with DP-0 deactivated and so far didn't spot
any problems.
Only at the very start, I could find these messages, but that was before
running kde:
[   14.404932] [drm:amdgpu_atombios_dp_link_train] *ERROR* displayport link
status failed
[   14.404939] [drm:amdgpu_atombios_dp_link_train] *ERROR* clock recovery
failed

Still, it's hard to tell for this kind of problem that occurs so randomly.

I'll have a search if I have another DP cable, so I can check that.