I recently had this very problem on my "go to" plane, changing of elevator trim. The difference is that my plane had wood rods with 2-56 rods.

Turns out that the Dubro metal clevice had worn the threads on the 2-56 wire just enough that it would jump a thread or two from time to time. Closer inspection revealed that the threads looked undamaged but when checked with calipers and a magnifying glass, they were indeed worn slightly.

In addition I discovered that the Dubro clevice was designed poorly when compared to Sullivan clevices. The Sullivan clevices lock at the seam, the Dubro clevices don't. I have now discaded all Dubro and similar clevices from my shop.