I have a relative who loves to tell the story of a school building's clocks that would show the wrong time every Monday morning. Turned out their janitor's new vacuum cleaner was putting interference on the power line and disrupting the master clock system's signal enough to require a manual reset. Problem went away after replacing the vacuum.

We had a tech support customer who called every few Mondays at 9am because their keyboard wasn't working.

The cleaner's vacuum cleaner would occasionally pull out the PS2 cord.

After the first call (or at latest the second), did they not learn to plug it back in themselves?

I wish I still had your high estimation of tech support customers.

I recall one where the cleaning crew would unplug a rack because the socket was right inside the door (and yes, they had keys).