Extruder drops when switching between parts

MKII just started having this problem. When printing a single part where no lifts of the extruder are required beyond moving to the next layer, it prints perfectly. But for instance, if I print two parts next to each other, each time a layer on one is finished and it goes to move to the next part, the extruder will drop quite a bit and hit the second part. Printing continues but there lots of layer shifts as you might imagine. Any ideas that’s going on?

Check the Z axis belt connector piece, see if the 3d printed parts is loosened or worn out.

Thank you. While I was checking that I saw that the belt was loose from some mods I did previously. Easy fix. Working great now.