DDJ RB: Master volume controls left pitch fader

Hello, 

After perfectly working and performing for more than a year my DDJ RB started acting weird. My master volume knob now controls the pitch fader on the left (I guess it's sending a wrong midi signal). I have reset all midi settings in rekordbox, reinstalled rekordbox, reinstalled drivers and rebooted the firmware in my ddj rb. Does anybody have any idea what causes this problem? 

Thanks in advance.

Andreas Porters