Do you mean that you need to re-focus after a move?
Or is it that the focus is not as good after re-focusing?
There can be tilt in the stage, that will give different focus across the image rather than different when you move.
There will be a change in z-position as you translate, and that will be noticeable at high magnification because the depth of focus is small. The flexure mechanism moves the stage sideways, keeping it parallel to the base. However as the legs are parallelograms the stage moves over the cap of a sphere. This is shown in