Is the Ball Count also increasing as the balls go through the trough? As it should stop on the 5th ball, if the Ball Count unit is working. It is possibly a bent trough switch, (the one between the ball return kicker and the shooter lane) also a possibility of a broken wire between the trough switch and the ball count unit, you will have to check these at least. Has the Ball Count jammed up?

It can also be out of position, a lot. There are 2 stops on the stepper gear on the backside, that have to open and close the switches/contacts on the backside of the unit.