The machine will occasionally incorrectly drive the conveyor motors, causing only one side of the conveyor to move. Markings have been applied to the conveyor drive wheels which makes the asymmetrical behaviour obvious.
This results in the PCB 'slipping' or 'jamming' and not moving into position properly, most noticeable when the board does not move into the correct position in zone 2 and the head cannot locate the fiducials. It may also result in a loaded board not moving all the way into zone 3 and getting caught in the board clamp in the following loading cycle.

The issue has been hard to reproduce, but happens very frequently during production runs and is a frustrating occurrence.