Thinking out loud so bear with me....
Attract mode is fine = Displays, Lamp Matrix, CPU all should be good. Displays don't care if your in attract or not. Lamp matrix must be OK or you would not see attract mode show.
Are you getting the usual 'click click' every 30 secs or so in attract as the relay turns on and off the lower playfield?
You are having the problems with factory and RD boards so it has to be non-cpu related. The the RD has it's own game rom so rule that out (would have been my first guess otherwise).
Normally when you hit start;
The machine resets
The Mozart starts looping
The bank targets all reset
The ball gets kicked out into the shooter lane
Are you getting the thuunk reset on the 5 bank?
My brain is telling me that the game code (both copies) must have a check they do just as they get ready to launch the ball into play and some check is failing.
Did you run the diagnostics and see if any switches are stuck close?
Did you manually test the outhole and trough switches during diags to ensure they can close?
Did you verify all power?
Maybe your fat orange cap is crap and when it goes and turns on all the coils/bank reset you voltages nosedive and cause the cpu to crash?