So I having issues with the anti backlash being hard to move with my hand on the Z axis. The Y and X which don't have the anti backlasth move fine. So with the z together it very difficult or impossible to turn by hand. I backed of the set screw and made several tests. Open to ideas.
A suggestion with the regular nut blocks when they are too tight is to chuck the screw in a drill and run the nut up and down a few times. May work, if not you might send a request for replacement to the shop as it sounds like a poorly manufactured nut.
Good Idea. I seems the top part or the thinner part works smothly. But the lower half or larger section is very tight.. I will send them a email ...