Thanks,DeltaMac,
I saw the „Error“ message, which could be more helpful. This is all in the internal drive.
I have great trouble with attributing the issue to a specific component.
I’ll scan the system logs. Maybe there will a clue there.
Today, I noticed that some folders and files have a forbidden symbol next to them. There is some, unhelpful pop-up text that says, "Error" but no more indication to what the symbol is referring. The folders and files seem to be totally normal.
Any ideas?