Pioneer DDJ-SX Cross fader problem

I purchased the DDJ-Sx about a year ago and have never had any problems till recent , so I'm trying to figure out if it's the software or the controller that's the problem . So the other night at my gig , I put the cross fader over to the right and noticed that both songs on the left deck and the right deck were both playing I could hear both tracks . So I turned off the controller and Virtual dJ and restarted and it was fine for the rest of the night . Any help on this or if any one else had the same problem ?