DJM 350

While using the DJM 350 with a pair of CDJ 350's on rekordbox it can happen at anytime the DJM 350 stops playing out. Rekordbox and the CDJ's are still working just no sound coming out of the mixer. If I press pause and then play the sound starts again. This happens maybe once or twice during a 5 hour gig on both channels.

any ideas welcome.