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)
That's strange.... Check that the spinner is not in the same column / row as the ball shooter..
I get a little confused how to read these, but if they go numerical down each column then spinner is in different column to ball shooter. Right / left flipper in same column as spinner