I use a Boss GE-7 (with the level halfway up) through the effect loop on my Triple XXX head. This week, as I was rehearsing with my band, the volume level suddenly went down. I unplugged the cables from the effect loop, and the amp played normally. Later on, I tried to put the effect back on, and the amp played normally, if like nothing never happened.

At first I thought maybe that I was using crappy instrument cables, and they should be replaced, but the whole experience was indeed very strange...

As anyone ever heard of an effect loop breaking down before?

I own a peavey XXX combo. Same thing happened to me but I was just playing my amp. I moved in a certain angle and the volume dropped. I thought something was wrong with the amp. I got a new cable and it never happened again. So I'm guessing it's the cables. The cable that I was first using was a cheap one.