So this is a puzzler: Twice now I've had, during the course of a show, one channel slowly and inexorably decline in levels by about 20 dB as time passes. The second time, first one channel faded, then the other followed an hour or so later. Nothing changes about the sound quality otherwise — it's as if I were slowly turning down the gain on one channel, except the M10 doesn't have the ability to do that for only one channel.
Chain in question is CA-14 cardioid mics > UBB > M10 mic input. The same setup worked fine at other times before and after the problem nights. I checked the 9-volt battery and it seems fine.
Any guesses, anyone? Or anything I can do to help diagnose it?