Something similar happened to me, but I think it was more of a ‘hardware’ problem, meaning fader on CH2 got stucked at +5db. Of course I didn’t notice it at first, so when I was changing my layers/FX/Mixes/GEQ settings from this CH2 fader got to +5db, causing nice feedback (because frequency band on GEQ was pushed really high :)). I just shut it down, pulled fader down a bit roughly, and it was working okay since then. So mine problem was a bit different than yours, but just to let you know about it:)
Greetings!