I've been getting this message for a while on boot. Game plays fine as far as I can tell so I've been putting this off. But I'd like to get it cleared up now. I go into switche test and neither flipper responds to the switch test. Magna save button does. oother switches respond.When I go to single switch test T3 Left Coin Slot D1 says open and flashes. When I move the left coin switch to embulate a coin pasing through it flashes to closed and when I let it go it goes back to open. I cant get any other switch to make the test respond. I've looked at the wiring and it looks good all the way to the board (coin door interface PCB). I can try swapping my board from DH to see if this changes anything.
Any other ideas?

Yes in T1 switch edges test even slowly pushing he flipper button does nothing. In T3 single switch test mode Left coin slot D1 registers open and nothing else will register.

Swapped in the board from DH and made no difference.

Got the flipper buttons to register in test mode. Reseated the ribbon cable to the flipper bpard in the back box. Not sure why they's work in the game but not in test mode but it did. Now I use the butting sin test mode. Right flipper buttin works correctly and registers both switches individually when I press the button slowly. Left flipper button only registers first opto F4 but not the second one F8. I'll check the opto and also see if when I press the button if its clearing the opto path.