One of the most interesting bugs I've seen was in a small Arm single board computer powered Lego robot. The robot would work fine for minutes at a time and then suddenly die. When used outside of the arena area it was designed for the problem went away.

We eventually traced the problem to the metallic tape used to define features in the arena. When the metal roller at the back of the robot touched this after a few minutes of operating it caused a static discharge which stopped the computer!