Is it as of the latest 13.04.1 update? That broke musical time stretch mode in Nuendo completely, and depending on certain actions, the clips will automatically change size on the timeline. It's totally fubared and I wonder if it's related to this.
Here's my post at Steinberg on the issue:
https://forums.steinberg.net/t/nuend...pletely/921832

So a clip will go to original tempo unexpectedly and be slow and out of time with everything, or other tracks will sound too slow as that imported clip might be too fast. I do not understand for the life of me how releases like this make it out the door.