I had an issue with one of mine, although I may have bent the set screw or done something to it. I don’t think so. It appeared to be slightly bend because as the Y axis it was on spun it would rub and ring a bit at times. When I ordered a bunch of spare parts I ordered a few of the acme nuts and I’ve since replaced it. However, when I went to replace it I had a hell of a time getting the new unit to thread on. In the end I had to lock the motors powered on briefly and use a wrench, so there was something slightly amiss with the threaded on my lead screw. Whether it was the screw that affected the original nut or the nut was maybe slightly cross threaded on the screw or otherwise was out of spec I don’t know, but I figured I’d mention it in case you get any more reports similar to Tristan’s.
-Jeff