I have a SBE that also will fail to feed certain shells after the first shot. It also leaves the second shell in the carrier partway toward the breech.
My observation is that when the shell exits the magazine, it slams back against the trigger guard and bounces forward. I think it should be caught by the small notch at the rear of the carrier latch and should stay back at the trigger guard until the bolt moves forward. This problem occurs most with Estate shells that have a large angle on the front of the case head rim.
I sent an email to Benelli but do not have a response.