UR 816 C Output Level Knob non-responsive

I alternate back and forth between using a UR22C and a UR816C (they are in two different locations). Recently after an extensive period utilizing the UR22C, I transitioned back to the UR816C. Upon opening a Cubase project file while connected to the UR 816 C, I am finding that the main output volume knob on the front of the UR 816 C is non-responsive. The output is set a Mix 1L and Mix 1R, I believe they are setup as the main output busses. I spent some time in dspMixFx and it appears to be set up with Mix 1L and Mix 1R designated as the main outputs. Any suggestions?