XDJ-R1 Stopping track for no reason

Mid set I had a track suddenly stop without warning. I then could not get any selected track, even ones previously played, to work on that channel (LHS) RHS working perfectly fine even with the track that the LHS originally stopped on. To get the channel to work again I had to turn off my XDJ-R1.

At the time I was using Remotebox to select my tracks via IPhone 4s from a USB HDD. All latest firmwares for XDJ-R1, Remotebox and Rekordbox.

Any ideas on what could of caused it and what I can do to stop it reoccurring.