Not a bad idea...but find out where that buzzing is coming from, it's not the magnet, you can hear the magnet hum when it's holding the ball, I think the buzz is coming from the diverter behind the sanctum, it maybe getting stuck when it's trying to lock the ball.

TS.JPG
See the metal diverter...I bet this is what's getting stuck, you may need to rebuild it.

I have no idea whose Shadow that is...I picked it up on the internet to help illustrate.

I just watched the video again, the machine knows when the 3rd ball is in the sanctum and it starts the multiball with only the one ball, so I have to say your machine thinks it's missing 2 balls....You need to take the balls out and put them in one by one in the switch test and make sure it's registering in the switch test matrix.
Also it happens 50% of times is because that's how trough optos go bad..they start working intermittently then eventually cut out. Here is an easy way to check if you have a flaky opto, put the game in the switch test and take the balls out, then with an open hand slap the pf and see if the switch matrix registers a switch from the shock. Let me know how this plays out..............

Opiated? Lol...ok. Funny but still wrong, if the diverter is kicking the ball out, which means then it know the ball is in the sanctum so the switch idea doesn't hold water. The only way it will kick the ball out rather than lock it is if it thinks theres only one ball in the machine. Besides if the switch was not fully engaging it would first go into ball search then kick out the ball...if you watch the video it shows the ball releasing from the sanctum immediately.

Then good luck fixing intermittent opto problems..I guess shot gunning parts is much better.

Great except you quoted my post and said that it was opiated, and then proceded to give the wrong advice of stuck switches, and criticizing slapping of the pf..which by the way is much softer on the pf than flying steel balls.

In that case my tip of the hat to Atomicboy. However, I thought you said that it kicked the same ball out without ever locking any....which made the stuck switch idea wrong. If the machine locked the first and then it triggered 2 switches then it would have started multiball with 2 balls not 1. Also easily the switch test would have indicated 2 switches closed on the martix, which would have tipped you off of a stuck switch, (thought you said you did this) but whatever. Good luck.