You may also try the empty magazine on the camera and testing the combination that way. The counter still works and you don't have to take anything apart. If it still stops, you can take the side off and watch it as you check it on the camera. There could be a loose bit wandering around it there.
FWIW both gears of the advance start and stop at the same point in their travel. They make one complete cycle, so it could be in the body too.