U-Mix Control Pro + Cross 3.3.1 crossfader issue?

Hi there,
I'm using a U-Mix Control Pro + Cross 3.3.1 and I am running into a weird crossfader issue. (OSX 10.11.4)
Everything starts off fine, but after a certain point (no identifiable trigger), the crossfader will stop going all the way to the left. i.e. it moves fine on the controller, but only goes 1/2 way to the left on the software.
(This means I cannot complete a mix unless I manually drop the level of the right channel; likewise, I cannot cue/preview right channel track without it bleeding into the monitor unless I drop the level to 0).
Unplugging/restarting sometimes fixes the issue, sometimes not.
Any suggestions?
LEN
I'm using a U-Mix Control Pro + Cross 3.3.1 and I am running into a weird crossfader issue. (OSX 10.11.4)
Everything starts off fine, but after a certain point (no identifiable trigger), the crossfader will stop going all the way to the left. i.e. it moves fine on the controller, but only goes 1/2 way to the left on the software.
(This means I cannot complete a mix unless I manually drop the level of the right channel; likewise, I cannot cue/preview right channel track without it bleeding into the monitor unless I drop the level to 0).
Unplugging/restarting sometimes fixes the issue, sometimes not.
Any suggestions?
LEN