I believe I found the problem. Operator error not working the press handle in the same way with the same pressure. I took the longer ones and re-seated them without moving the die adjustment and they seated correctly. I seated another batch while paying closer attention to working the press handle and they all seated the same.
This is a very common issue. See my first postAnd is it just possible that the stem in his die doesn't match the variation in the nose lengths of the bullets the OP is using ? That variation in the nose length may be bottoming out in the stem , on some bullets , causing the seating depth issue .