Has anyone experienced this?

I have only had the new unit for about a month or so. I've been using it for woodshedding at home and rehearsals and a couple of live sets every sunday.

But never have plugged the 1/4" out into the front end of my amp till rehearsal last week. I switched from "Line out" to "Amp" on the front of the unit and plugged in

to check it out. After about half an hour or so the volume went to half and stayed there. I made no changes to the patch or any settings whatsoever.

Got an Idea of what happened????