CDJ-900 Loop is off beat

I notice that when I'm looping in on my CDJ 900 and beat matching to my other CDJ 900 I have the loop perfectly beat matched at the exact same BPM but than after a couple bars the beats no longer match. I noticed that just listening to the loop the timing is off. For example a loop that is supposed to be 4 bars ends up being about 4.1 bars and not flowing smoothly there is a little pause before the re-loop which puts my loops out of time and makes them sound bad. Is this a malfunction with the product and is there anything I can do?