I'll throw another vote in for improper seat.

I ran into the same thing when speer changed the primer well dimensions on the 357sig Lazy S brass. I had been using CCI's with a nickle coating. when they changed it the well was so tight that not only did they not seat all the way sometimes, sometime they would just crush.

I think I replaced every spring on two guns before I figured that one out.

the reason the primer doesn't go off is that when the pin hits, if the anvil isn't seated against the bottom of the well it just knocks the anvil down and then you've already got a dent and there's nothing between the cup and the anvil to go ignite.