I remembered more than one relay is activated at power up. I just took a quick look inside my coin door and powered up. If you manually reset the bank.. ZB, QB1 and QB2 will latch at power up.

If you look at the left side of your schematic under "control bank", you will notice the QB2 is not a relay. It is physically attached to the QB1 relay and acts as additional points for the same function. Therefore, your problem lies with QB1. You might want to clean the points of QB1 and R. I am not familiar with how long you have had this machine, but when I get a machine that does not work.. I generally spend some time cleaning "all" points. Yes, it may take some time.. but it sure cuts down the debugging time trying to figure out a multitude of problems. Not to mention the problems that arise shortly after you get that kind of a machine running again.

QB1 Problem (resized).jpg

Just a hunch.. QB1 is turned on by XB (Last ball relay) && O (Ball return relay). Any chance the ball counter isn't being reset?? I think if its on the last ball in the player unit, it would act this way. Have you cleaned the contacts on the player unit, checked alignment and proper stepping function?

QB1 Problem2 (resized).jpg

"I get this far and though it says "O" locks in the next step the act of locking might be for one second so I can’t say for sure if it locks or not but it does energize and the score motor comes on for 1/3 of a rotation. At this point the game goes to game over. The ball return coil does not energize and receives no power to do so."

Is QB1 latching when this happens?? If so, it would cut power to "O"

At the end of the fifth ball, my machine lights up the player "2" after scoring the bonus even though it was only in single player mode. Is this happening on ball 1?? Have you tried both settings of 3 ball or 5 ball?