WEDJ + DDJ-200 headphones always playing Master, not cue

I have Split Cue switched on in settings but the headphones always play exactly what's coming out of the speakers regardless of what I select to cue.

The splitter hardware is working fine - I've tried listening to right/left test audio and it works as expected (left through speakers and right through phones). Split Cue also works fine in Djay.

So from what I can tell, it seems to be a problem with WEDJ. Any advice? Or should I abandon it in favour of Djay? (I'd prefer not to!)

Thanks!