I had a similar problem and it turned out to be the lead screw. The lead screws could be dirty (if so: clean and re-grease) or there might be a fault in the thread. You could try and turn them around (upside down) and see if the problem persists. If the thread turns out to be the reason you can either accept the artifact on very high prints or consider changing out the faulty leadscrew(s).
I had a similar problem and it turned out to be the lead screw. The lead screws could be dirty (if so: clean and re-grease) or there might be a fault in the thread. You could try and turn them around (upside down) and see if the problem persists. If the thread turns out to be the reason you can either accept the artifact on very high prints or consider changing out the faulty leadscrew(s).
I replaced the lead screws and the nuts they are brand new. I did find an issue with the old ones. So it is obviously something else