Two initial thoughts:

1) Are there any custom orchestrations for Diner on the PinSound Community site? If so, download one of those already-done mixes and try it. (When I did my GNR mix I started with the original legacy orchestration and found a bunch of the sounds were in the wrong folders, so sounds wouldn’t fire when called, stopped early or overstepped other sounds.)

2) Your problem sounds somewhat similar to the power problems common to Data East installs - under heavy load, sounds would cut out and stop completely. Maybe post a video of gameplay so we can see/hear what's going on.