Your game doesn't know what in heck a diverter is. It does know switches.

Open the diverter and roll a ball through. The first switch the ball goes over is the issue. My guess would be the switch arm that comes up through the playfield isn't centered in the slot and may be rubbing on one side. If so it acts slow and the game ignores it in game play. If that is okay, it may need adjusting so when a ball comes through it hits the switch good every time.

The error will go away with game play.

LTG : )

That gate back there the ball goes through when the diverter is closed, be sure it's switch isn't stuck closed and registering a hit when it shouldn't.
LTG : )

With the high power interlock enabled, test on 35 should briefly snap it open and the spring snaps it closed.

If yours doesn't do this, please check for broken wire at the coil, cold solder joint. The thin wires from coil to coil lug, dig around them for a crack or break.

LTG : )

Not the normal fix. Good job working through it !

LTG : )