Has this happened befor with this die? If so, check the size of the expander ball. If it is to large the manufaqcturer will probably send a new one free. My FL die is RCBS and right at the top of the expander it measures .241".
Guess I can see where the ball might get smaller as a result of wear, but how would it get bigger? I get the impression it worked previously. "Ran them trough the die like normal"
If the ball were crushed, it would be out of round but still should not create a loose bullet situation.
If the depriming pin / expander ball rod were bent, being pushed through and removed at an angle, I could see where it might cause the described problem. A micromete would show an oblong neck. Though in my experience, if the die is dropped or the depriming pin runs into something solid, it snaps off the depriming pin rather than bending the rod.
If its a new box of bullets, you might check the bullet diameters to make sure the bullets are the correct diameter. If they are not, manufacturing flaw or possible miss label of the box?
Maybe something stuck to the ball?
Too much lube? But most don't use lube when neck sizing.
Dirty brass? Shoving the expander through a fouled neck?
Moose calling can get confusing to some, but cow calling is your main tool when moose hunting. If you go out and buy moose calls I would say you're wasting your money unless it is the birch bark cone. I find most store bought moose calls sounding worse than puffing a grunt your hands to make the call. You can roll up a piece of birch bark in a cone shape to use as a call and spend your money on a video that teaches you the basics of a cow call. A milk jug or a coffee can with a hole and a rope...