There was this old fashioned vending machine at college. Something about the tube the cans dropped through would flawlessly catch the can and get it stuck. The next can along would always reliably knock it free, but get stuck itself. You'd see your can get released and drop, but an entirely different one would turn up at the bottom. It was a bit of a pain but rather fun anyway so no one was too bothered. Eventually one of the cafeteria ladies opened it up and fixed something.
Perhaps some of you could benefit from a check up from the cafeteria lady?