I have the same problem, bought it B stock and yeah, it's a hardware problem. I made a ticket to know what the issue is, because it's coded in the firmware to show "04" when something's wrong, it doesn't show a fixed "99" like it's stuck on a value, is like not recognizing the pedal, maybe this "something" could lead to a fix.
Hi I bought a B stock Amplifi FX100, it was almost new but the volume/wah pedal didn't work. Tried calibrating it but after step 3 it shows "04" not "99" as the video tutorial says. BTW, the pedal button works fine (switching between wah and volume). Has anyone this problem? Is there a way to fix it? Thanks