[OPEN] CDJ-2000nxs + 900NXS mixer audio balance swapping from left to right on recording ?

Strange technical bug, please help if anybody knows. Im using 2 x CDJ-2000NXS with 900NX mixer, im using the digital out on both cdjs to the mixer then the USB to record a set direct to the latest version of Traktor, however on every set at around 5-10 minutes in the balance moves from left to right, im not pressing anything to get this, you can see it in the waveform below just past the orange marker, I dont think it comes out of the mixer live channels to speakers, well not noticed anyway, any clues ?? Cheers DJs of the world ;0)

Stu K