Many pinball machines has problems with ejecting the right number of balls to the shooter lane, and Xenon is no exception. Actually, I think Xenon is a prime candidate for this problem.
I also had problems with my Xenon. It would eject two balls to the shooter lane, at different times.
Unable to find a previous solution, I found that redesigning the ball through beneath the apron worked for me. Like all pinball machines, Xenon has a switch to feel if there is a ball in the out hole. It also has a switch next to the shooter lane, close to the half-moon-ball-transport mech. But what Xenon also has, is a switch between the two; it seems to be present to feel if a ball is en route to the half moon mech.
My thought were to remove the ‘pass-thru’ switch and replace the (leaf) switch by the half moon mech with a microswitch. Yes, I hate leaf switches.
Here is a picture of the modified ball through.