As a temp work around you could use it on master or a single channel..if the mixers out of waranty I would start by checking all internals are connected properly, ribbon cables ect. If you gig the mixer it's possible something is loose. Failing that replace the level/depth pot and the tac switch under the flashing on off button.
Also a firmware re flash might be worth a shot.
A new firmware for the KUVO compatability was released find it here in the support section.
All though it's not directly related a re flash of the firmware may cure it.