Replace ALL the balls after work? Go in test and check your trough switches for sure, Unplug and replug if you can. Check all those and the shooter lane swtich

Sounds like one of your trough switches is flaking out, or divots in the trough 'floor' plate letting balls get stuck. Something like that...

My thoughts are the trough optos. Make sure they all test out. Also, its strange that you are still in gameplay and the drop target is not going down when hit. Though this could be just a result of the auto plunge disabling it. Is this starting when you drain a ball or just randomly during play?

Currently got the exact same issue with endless balls , although I can hear the right diverter clicking under the playfield all the time so was going to investigate that. Keep us posted how you get on

call my brother Tim 574 361 9386, mine did the same thing but I can remember what he did to fix it
plus, Im not technical

It's an opto. Pull all 3 VUKs and clean all the optos. The machine is reading one of the optos as closed and kicking the ball out because you have "too many balls in the machine"

Put on switch test and roll a ball down there and it should activate optos 1 at a time.
Switch level test will show you active switches and look to see if one trough is diff'rent.

If it's board related, it would be the trough opto boards. They're screwed directly to the ball trough and keep track of how many balls are in the trough. I had a problem about every six months with mine. Since the boards are attached directly to the trough, they get a lot of vibration from the launcher solenoids. There are upgraded replacement boards made by Great Lakes Modular. When I got mine a few months ago, I believe PB Resource had the best price.

Yep, and connected with molex connector that should taken off then put back on then run tests above

Like others have said it's very likely your trough opto boards you can buy a new set from Great Lakes modular for 60$ . Also make sure if you replace these boards the connectors going to them are in good shape

Did you try cleaning the optos with windex and cutips yet?
It may save you from having to buy another board.

Nice, that looks like it's off the trouth board. Pull the front board and see if you have 7 of those soldered to the board. Betting you only have 6 and that one needs to be soldered back on.

Go to great lakes modular website look under products the part number is DCS-TBS widebody trough opto board set