Tempo Issues with beatport aiff files, XDJ RX2 & CDJ 2000 Nexus

I recently started buying music from beatport, at first on WAV format and more recently I opted for AIFF due to the tag compatibility on IOS. 

Last week as I was playing on my XDJ RX2, the tempo slightly moved up and down while playing my newly bought AIFF tracks. Thought this may be an issue with the RX2. A day after I played at a bar on the CDJ 2000 nexus, same Issue with slight tempo jumps on the AIFF files. 

This makes me believe its either the files or my usb flash drive.

Has anyone encountered similar issues? Thanks.