Have you given the screw a very good inspection for any damage in that area?
It could be something like a bit of dirt in the ballnut, but I'd expect that to cause jamming at more than one position.
Have you tried giving the ballnut a good grease, then running it back and forth fairly slowly to work the excess grease out, and seeing if any dirt comes out with the grease?

Are they closed loop steppers?
It could be something like a broken wire, that only looses contact when the cable is flexed in a certain position, but I'd expect that to get worse over time, and to trigger a fault in the driver.
Might be worth removing the wiring from the cable chain, and if there's no obvious issue with the wiring, running the axis with the cable just held to so it's flexing in a different way.

Failing that, you're probably looking at a full strip down of the nut, to ensure that there is no bits of dirt/swarf in it, but that can be quite an involved job, especially if it uses alternate sized balls, and as your screws are multi-lead, there's going to be a few bearing tracts to clean/reload!