Three areas would cause the problem (besides ammo that is to lite).
1) recoil spring is damaged, worn, or rusted.
2 bolt doesn't have enough lube to freely move, maybe dirty?
3 ejector broken.
Couple of questions for you:
Is the shell fully leaving the barrel but not fully exiting the chamber?
How far back is the bolt coming (1/2, 3/4 of the way back to the rear?)
Does it do it with different brands of ammo or just one?
Is the action butter smooth when you cycle it (unloaded)?
The more you describe the better I might be able to give you advice. But, the three suggestions are what I have seen others have when they act up.
I have heard that benelli service is very good. My friend sent in his H&K a few year ago. They replaced 6 parts that he didn't even know were broke. Never charged him a dime. I just called them a month ago and they over nighted me a recoil spring, nut that hold it in the recoil tube and a few other parts for free.
You can PM me if you like.
The only thing worse than being blind is having sight with no vision- Helen Keller