There is a specific timing of everything. Though not much you can change on your own, other than replacing the action spring, which I think was among one of my first suggestions.
Firing pin hits primer. Primer ignites powder which builds pressure and forces the wad and shot down the bore. In that time, the hull also expands to the inside surface of the chamber and forms a temporary gas seal. Where it stays expanded for some time until the pressure reduces.
If the bolt tries to extract the hull too soon while the pressure is still high in the barrel, it could rip the base off of the shell, which again as I mentioned, change the action spring first.
This can happen in other firearms too. Just research "case head seperation". That's actually the technical term for what is happening.
Again, please pardon my lack of knowledge, but is there some sort of “ timing” before the mechanism pulls the shell back for ejection? Since the thin plastic hull is staying in the chamber while the rest of it is ejected, is it possible for the extraction to begin before the load has fully cleared the hull, albeit instantly, thus causing a swage effect, pinning the plastic to the bore as the hot brass is jerked backwards? Could a weak or collapsing wad cause a momentary delay? Also, wasn’t it mentioned that some of the shells were loose or the hulls rotate in the brass? I can’t imagine that is normal..