Reply to Loops knocking themselves out of sync in Pro 2 Help

I am having a problem with loops in traktor Pro 2 while in sync.

The problem i am having is the tracks in question change BPM/Tempo half way through I have beatgrid in time at the start of the track so it mixes in time/sync however when i loop it, everytime it loops round it knocks itself out of time/phase fractional and keep doing it so it goes further and further out of sync.

Anyone else had this problem?

I have just upgraded my laptop and on my old on i never had this problem.

Are there any settings i am missing?

Cheers