One of my favorite pieces of debug folklore was the story of a minicomputer or some other serious machine rebooting in the middle of the night. I can't remember exactly but it was in some university during the 70s/80s. An important server would spontaneously reboot in the middle of the night on some days but not all. Finally, someone sat up all night to watch what happens and observed a cleaning lady unplugging the m…
Eventually, we discovered that the young girl that was responsible for changing all the prices was using the server room as her makeshift office. She would stick all her magnetic clipboards with the upcoming price changes to the side of the server. When she heard the tech was coming she would clear out all her stuff since she knew no one was supposed to be in there. The magnets were wreaking havoc on the disks causing the errors. The store manager got her some proper office space and the errors went away.