Reseat connectors at the trough. Stern is notorious for loose trough connections, especially if you have a shaker.

Also, ensure the auto launcher and plunger tip are centered on the ball. Remove and reseat the plunger assembly if necessary. The good news is that these things are usually easily fixable.

The trough is what holds your balls. Pull and reseat all of the connections. If you have a shaker, this is likely the culprit if it's spitting out 2 balls.

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Finally, make sure the rubber plunger tip isn't touching the ball when it's in the shooter lane. This will cause a weak auto plunge.

This happens on every Stern game. It's the ball trough connectors.

If you want to get fancy, replace the existing IDC connectors with Molex connectors and you probably won't have this issue again. Or, you can just take off the connectors and solder the wires directly (although this is probably harder dexterity-wise than replacing the connectors).

Post another message if you want more info on how to do either of those.

(But as said above, it'll probably work to just reseat them. I've even rubber banded them tight so they don't loosen. Not as good of a long term solution as either of my above suggestions.)

Upload a picture of your shooter lane with a ball in it. Your auto launcher may be crooked.

Check the wire on the shooter lane switch. That happened with my Avengers. It eventually just broke & the problem was more obvious.

Upload a picture from the top that shows the ball in the shooter lane. This will show if the auto launcher is centered and how far the plunger tip is located from the ball.

Something just happened to me last week and I thought it might be worth mentioning. Checking plunger and autolaunhcer alignment is important. You may want to check to see if the little blue rubber piece on the coil that fires you're auto launcher is broken. Had a similar issue with BDK and when the machine was trying to launch two balls, but blue rubber piece broke/cracked and my auto launcher sometimes didn't have much power to it. It wasn't obvious until I manually pushed the coil up and down and the cracked piece fell off.

I think you're looking at the wrong thing. Your photos focus on the three black ball through switches. The opto connectors are those white connectors. One side of the optos has a 3 pin connector, and the other side is 2 connectors.

Your comment said: "They were properly seated and soldered".

You can't just visually tell if something is seated properly. You need to pull the connector off, and then just push it back into place. That's what "re-seating" is. Those white IDC connectors are flakey...even on new games. They are for the optos, one which tells if there is a ball ready to be ejected, and another, higher one which tells if a ball is balanced halfway up (ie "jammed").

When a ball is not jammed, the opto shines all the way through. If a ball is jammed, it blocks the opto, and the game knows to try and kick it out into the shooter lane. If the connector loses connection, then the opto does not shine through, and it thinks a ball is jammed, so it tries to kick it out.

So, if the connector is not secure, it will kick out a ball at the start of a ball, then think one is jammed, and then kick out another...and you end up with two balls in the trough.

Re-seat the white connectors by taking them off and putting them back on. This takes 5 seconds to do by hand. In my experience, this will always be a problem until you get rid of the white IDC connectors by soldering the wires directly, or by switching to molex connectors. But for now, you can just reach under and re-seat them to fix the problem of 2 balls in the trough.

Perform a coil test and watch the auto launcher. If it's slow or sluggish, check for flaky connections or anything getting caught on the launcher.

Watch the ball go into the trough. I've seen it happen where the machine isn't leveled properly (too flat) the ball goes into the shooter lane, bounces up a bit and the launch is hitting it before it's up against it.

Have you replaced the coil sleeve on the auto-plunger? To do this, you take the coil off (by removing the nuts in the middle of its bracket) and then take out the plastic sleeve that goes through the middle of the coil, and replace it.

If it's dirty, the plunger can get slowed by the dirt as it gets pulled through. It's also possible the plunger itself needs to be replaced if it's all beat up.

on my DE tmnt the autoplunger wouldnt have enough punch sometimes
it turned out to be the rollover in front of the plunger the one you see on your picture

the ball had launched from the ball out against the rollover switch and it warped a little
when the autoplunger launched the ball the rolover switch klicks but then rapidly clicks again so autoplunger losts power

bended rollover a little and the problem was fixed

maybe this is your problem to???

good luck