DDJ-GRV6 cue volumes not functioning when DDJ-FLX4 does with the same settings

I've just upgraded from the FLX4 to a GRV6 and encountered a major issue that the cue function doesn't work correctly on the new controller.

Key issues:
1. Headphone Level knob doesn't change the cue/phones volume at all
2. Headphone Mix knob between cue/master doesn't adjust the mix at all
3. Master Cue button does nothing at all. When enabled it doesn't cue master as you would expect. On or off also makes no difference to issues 1 & 2.

Turning these knobs doesn't even register in the Rekordbox software as the icons highlighted below don't move at all when adjusted on the controller.

When I adjust the digital knobs (using my mouse to change it in Rekordbox) the outputs work as expected. It seems to be an issue of the knobs on the hardware not "talking" to the software.

I am using an audio interface (UR24c) to enable the use of studio monitors, which I had set up to work perfectly with the FLX4 (Normal use, none of the above issues, knobs work to affect the software). Now using the exact same settings with the GRV6 I'm encountering the problems above.
Please can someone help me resolve this?