Rekordbox - Headphone cue only playing out of one side

Hi Guys

I have a DDJ-200 a I'm using a Behringer UMC22 external soundcard which has a L and R master ouput. Instead of the splitter cable provided i am using the L output for the master and the R output for the headphones which works for the cue vs master sound ouputs (i.e. cued songs play out the headphones and not the master speaker).

However when the cued song is playing out of the headphones it only plays out of one side of the headphones. I have tried with mono output on and off and its the same both ways. Its driving me nuts can someone please help me lol.