OK, after another hour of trying to reproduce manually what happened (although it didn't reset the game this time) I observed a bit of an oddity.

When the Lt Decker spinner is going and if you press flippers - the ball shooter will fire once.

I don't know if this is a feature or some sort of weird problem.  I had previously changed the diode on the ball shooter, but will also now change the one on the spinner too....

Update....replaced spinner diode...nil value.

Game has not reset, but I dont think the ball shooter should be firing when spinner is going! (with flippers)