Xone K2: 3rd fader stopped working, 2nd fader sending signals to 3rd fader

Last gig my xone k2 3rd channel fader stopped responding; however, when i move the 2nd channel, 50% of its motion shows up on the 3rd channel, so:

100% volume channel 2 = 75% volume channel 3

0% volume channel 2 = 25% volume channel 3

I’ve tested on 2 separate computers running mixxx, firmware update to latest, midi map reset to default.

Any Ideas?

p.s. the xone k2 test software on windows shows movement on channel 2 but no movement on channel 3