When using the API controllers in Max for live, it seems that it is not possible to control the Master track crossfader. In fact, visually it seems controlled, but it has no effect on the audio.

crossfader-control-via-api

Have you checked that the tracks are correctly assigned to channel A/B in Live?

mastertrack crossfader control flakeyness is a known issue, and apparently ableton are looking into it.

Crossfader control via API