Sure sounds like some switches/optos are not working. Game relies on these switches to fire coils and keep track of balls. I would go into the switch test and test every switch in the game. The manual will help to locate all switches. Maybe some switches just need adjusting or optos cleaned.

My DH had an issue with the connectors on the 12v board under the middle of the playfield that supplies the optos. I received trifurcon pins and a new connector.housing and have never had the issue again. Check there. Could just be cracked solder on a connector but I question the pins as well. They get cooked and oxidized.

Before you start tearing everything apart, make sure to check that the balls are all moving forward down in the ball trough. Sometimes on mine they get a little sticky and don’t slide all the way forward. The Optos don’t sense them and starts the search for them. This started happening when I added shiny new balls.

Sorry, I should have read your post carefully before I replied. Might be faulty optos or maybe needs a cleaning. Try cleaning the optos before you start replacing them.