Glenn...
Weird things happen. Twice I lost the total audio signal from the keyboard. Turning it off and on again corrected it. Why? Dunno!

The only times I have experienced a drop in volume... it was because I accidentally hit the fade or talk buttons. (operator error)

Sorry to hear about your voice. I had a similar situation the last couple of weeks, which I think was allergy related. I eased up on the vocals, drank lots of tea & honey, gargled with gargly stuff...and it is much better now. Good luck with yours.

Eddie