Very helpful, 'Dude!

Frank... is the problem repeatable? Do the same songs do it each time? (might be an issue with some sys-ex or a fadeout in the SMF)

Alternatively, did you accidentally hit the fadeout button? Or do you have fadeout assigned to D-Beam or F/S for that UPG?

First thing I'd do is backup your UPS and UPG's, then do a Factory Reset then load back the data. Then use those UPG's again.

It might be something different, but it sounds all the world like you accidentally triggered fade-out.