Pioneer CDJ 900 slipping out of time after Beatmatching.

Hi there

My problem is simple, on approximately 60% of my music (All rekordbox analysed through 2 and newer 3 edition), the right hand side CDJ will play slower than the left. I play two songs of the same BPM, beat match them fine, then approximately 15 seconds after I will notice it slowly slipping out of time, after approximately 1 minute, the tune's are completely out of sync.

I've had this problem for a good few weeks now, I've tried everything I can think of. I've reanalysed my entire collection numerous times, i've tried analysing it in both versions of Rekordbox to no avail. 

Any help will be extremely appreciated. 

This all started when I updated to Rekordbox 3.

HELP ME PLEASE