I think the issue may be that very first switch in the multi-ball trough. That switch ejects a ball when it is triggered, and if it does not click down all the way, they'll just pile up and do not shoot out.
I had to bend it upward slightly to get it to catch when the balls would drop into the trough. It may just need a small adjustment, or you could try and run a longer/different wire. It uses one of those little c-clamps to hold the wire in place, so you can thread a new wire through the switch and bend it to whatever shape works best to actuate the switch. I use galvanized steel wire that comes in rolls from Lowes.
Those trough switches are about as finicky as the T-Rex switches on JP. I spent a good hour playing with them until it worked consistently when I had it.
As for the pile-ups, sometimes that would just happen due to two or more balls draining and hitting that area simultaneously. It is hard for that outhole kicker to launch a ball when another one is butted up right against it, and it can affect how the ball lies in the trough and activates the switch there. Not sure how to remedy that. I'm sure another Centaur owner here has an idea to prevent pile-ups.