I suspect those parts are not getting logically placed to 3 different conveyors (or motion paths in them), but only 1 or 2.
If the components are on same motion path they can initially overlap but the motion planning will try to separate them from each other physically when moving.
You can see which component each part is attached to by using the PnP tool (shows blue arrow to parent comp), or use the Inspector add-on to see which container / motion path behavior the component is actually in.