Sometimes my MC3 is unhappy with my expression pedal in the heel position. It’ll be a smooth and stable taper until I hit 0%, then it will continually jump to 100% and back without being touched. No amount of calibrating will fix this. I can get the problem to go away with repeated power cycling and/or unplugging /replugging the expression jack.
I’m confident this is an MC3 issue because I’ve tried several different TRS cables and the expression pedal doesn’t give me this problem when connected to other pedals.
seems just like this MC8 problem here: MC8 Expression Pedal on FW 3.11.1 EXP flickering to 100% and back to 0% when no pedal movement - #7 by adamqlw