If I remember correct those dts wire in series so when they all go down the last one completes the path to the board to trigger the coil to reset the bank. Check under the drops to see if there is a loose wire.

No loose wires then time to make sure all the switch contacts are clean and making good contact. Game off. Drop them all. Lift pf. Put ohm meter across each dt switch and see if they buzz on your meter. May find one that isn't making continuity or makes continuity intermittent. How long has it been since the assembly has been pulled from the game and cleaned up? Any of the drops drag and not snappy when hit? Might be time to pull the assembly and do a thorough cleaning. Not for the faint of heart tho. But if you have slow drops this is the perfect oportunity to get the assembly out and really get to work on the hole thing. But I'm crazy like that. Make sure all the switches are working and adjusted well. Also, check continuity across all switches while they are raised. If one is stuck closed I wouldn't put it past the thing to ignore the switch since it's always closed. I doubt it but I've seen some weird stuff.

Screw it. Change the diode on every switch associated with the misfires.i used to check them is I had a suspect. After having so may testing good but still acting up after testing good and having to replace anyway I now rarely test if I suspect. They can test good and still be bad. Replace them, take care to place the band on the same orientation the old one came out. Do it and be done with it. Report back. If that ain't it you got more issues. BTW balls are good for doing phantom fires. You should go ahead and change the little green capacitors on the switches. They short and cause havoc as well. Someone correct me of I'm wrong but aren't the 0.05 farad?

Microfarad not farad