Comment by astrobe_

Indeed. A timing problem was my first thought when I read the title which was obviously provocative, maybe that's because I deal with timing problems often so I got lucky there, but I rejected the idea, thinking the user would have noticed it too. Nope.

I used to do some help desk as part of my dev job, and from my experience, users easily assign any random fact as the source of the problem. Often things like "correlation is causation" or *post hoc ergo propter hoc" (after that, therefore because of that). Good as heuristics, but bad when they are substitutes for reasoning.

Users cannot diagnose at all because they have no idea of how the thing they are using works (which often normal - we are the engineers, they are the users) (in this regard, users that think they know "that stuff" are among the most difficult to deal with). One cannot properly diagnose something one doesn't understand well.