Remove the balls from the machine and go to the Active Switches section in CPU diagnostics.

Most likely you have a ball through switch stucked closed.

I had the same exact problem on my Robocop. It's a very simple fix. You just need to adjust the metal leaf on the suspect micro switch.

It's possible that it only occasionally sticks. It's also possible that one of the switches isn't springing up fast enough.

Try inserting the balls in one at a time into the through in a regular switch test. You can also manually eject the balls out, since the through kicker is disabled during a switch test and see if the switches turn off after they eject.

On my Robocop, the issue would only occasionally occur, but over time it gradually got worse. In the end, it turned out that Through Switch #3 (the one at the kicker) was sticking down at times due to a bent out leaf on the microswitch.

You're welcome! I'm glad that you were able to find and fix the problem.