DDJ-SX2 crossfader assign B losing sound !

Crossfader assign B is dropping sound. It will play for a second but then will suddenly lose sound. If I keep it in "thru" , eliminating the crossfader it will play sound fine but as soon as I switch it to B it plays for a second and loses the sound again. I am a hiphop dj and do a good amount of scratching so this is a major headache. Please help! I can't find anything related to this