The connectors at ball through usually cause these. Try reseating them. Also there are a couple threads on pinside about this issue. Had it happen on all my Stern games.

Also use some lock tite on your bell ball. It will back off and hit the playfield. Owners club thread has a lot more tips .

Wish I could be more helpful. The threads are there but not sure how they are titled. This is a common problem on newer sterns .

Lock tite . It is used to keep threads from backing off. The ball unthreads down and rubs against playfield.

Search metallica detecting false ball drains for your issue. Hope this helps.

I had the same problem. Fixed it with dielectric connector grease.

Here is a thread on the topic:

https://pinside.com/pinball/forum/topic/acdc-premiumle-ends-ball-mid-ball

Is this the same type grease for automotive lite bulbs to resist corrosion?

This happens on Sterns, especially games with shakers. I've pulled and reseated the connectors with success.

Yes it is. And that is why it works here. It prevents the tiniest amount of oxidation on the connector pins which eventually builds up and causes connection problems. You can fix the problem temporarily by "reseating" the connector. Reseating causes the pins to wear through the oxidation and then they make contact again for a few weeks until the oxidation comes back. The grease prevents the oxidation from forming so the problem never comes back. Mine has been working for almost a year with no further problems. before using the grease, every few weeks the problem would come back. I reseated those stupid connectors probably ten times over the months where the problem kept coming back. I also had a similar problem with the connectors for the opto on the lower playfield. Greasing them fixed that as well. as they say - just a dab will do ya! I used a toothpick to put just the tiniest amount on each connector pin and then worked the connector on and off a few times to distribut ethe grease. There is so little grease, you would not even notice it when the connector is off.

There should be two connectors. One on the front of the opto board easily viewable and one on the backside. With the game powered down, take them out then firmly seat them back into place. Voila you can now have the game kick your ass and drain the proper way for you again

Don't just seat them back into place...PUSH them so the connector base on the trough board slides down the prongs a bit....you'll have a much better connection that won't get loose as easy. Problem solved.

If you don't put the grease on the pins, you will be doing this again and again. It is not that hard to do, so its not a big deal until you are having the best game of your life and the ball drains for no reason.

Just a note on dielectric grease. I've found big huge tubes of it for great prices at truck repair shops. Truckers use this stuff all the time so their prices are way better than getting it at a car parts store.