If you have it in tournament mode there's a bug regarding ball locks in the eye that can cause issues. If you are not in tournament mode, then do a factory reset and see if that helps.

Nope. The diverter is just a pivoting piece of metal and is not connected to anything electrical...just a post and a screw. If you locked a ball in the left eye, and you ended your game, when you go to lock the ball for the first time the next game it will go into the right eye first. The ball going into one eye moves the diverter to allow the ball to go to the other eye. The ball is the only thing that moves the diverter as it goes past.

Go to tests and rotate the head around the to eye side. Then go into switch edge tests. Take a ball and some sort of magnet and place the ball in an eye and remove with the magnet and replace/remove several times to make sure it registers every time. Do the same for the other eye. I'd do this at least 20-30 times.

If it registers anything different than the eye you are placing the ball in or is doesn't register 100% of the time then remove the helmet, and the screws holding the face. Look for a broken wire or diode on the switch. It could also be that the actuator wire needs rebending so the switch registers. Check the connector under the playfield to make sure the connectors are connected and the wires look good.