Bug that only showed up when I was not watching

I had a bug that reproduced about once a week and never when I was looking for it. My tests passed. My logs were clean. Then I would get an email from a user describing something that should have been impossible.

I could not see it for a month. And then I caught it because I happened to leave a terminal open overnight and came back to a strange line of output.

The bug had been there the whole time. I just never looked at the moment it happened, because I was only ever looking during the hours when it did not.

This is the trouble with intermittent problems. They are not rare. They are just rare in your presence, which makes them feel unreal, which makes you stop believing the people who report them.

I do not have a method for this. I just try to trust the report a little more before I start doubting the person.

Have you ever spent weeks on an intermittent bug? And did it make you slower to doubt the next report?