I had this problem yesterday, narrowed it down to a guitar cable that was at least 30 years old hadn't been used in 28 years! Seemed to work, except level would drop of then come back and fade. I just wanted to utilize some old cables, not anymore! Rigged it with recent cables and went off to my gig last night without a hitch.
One thing that happened first was moving from patch C3 back to A2
I noticed every patch I scrolled through had the wrong details on the screen. Shut off the unit, turned it on and the screen was back to normal, then the audio problem. Now everything works with good cabling.