Replicator 2x vertical shift

Hi! We have a vertical shift. Please see this video clip (30Mb) share.reidal.com/replicator2x.mp4

This occurs always at the same location at the printed model. It doesn't matter where if I move the model at the printing base plate. The shift occurs many times during the printing job.
I have tried to tighten the belt, added new firmware, reset to factory defaults....

Any idea?

Cheers Daniel

I tried watching your video on both my work computer and my home computer and I was never able to see the entire clip.