Cue is not routing to my headphones?

Hey, 

I am using Traktor with my controller and when I press the cue on my DDJ-SX2 it doesn't rout to my headphones, it still plays the track out of my monitors?

It has been working fine and now all of a sudden doesn't, pretty sure I must've changed a setting or something but I have tried all of the suggestions I can find on the internet and nothing seems to work?

Someone please help!