Help please

Are you positive the chamber is long enough? Sounds like the crimp is opening beyond the chamber, and sticking the shell. I ran into a similar situation firing a 3 inch in a 2 3/4 gun. Jammed it tight. Pressure was pretty high too.

Are you able to open the bolt? If so, make sure your extractors are clean and not broken. A Mossberg is known for good extraction.
If the bolt is stuck with the shell, clean the heck out of your chamber, maybe even hone it with an automotive drum brake wheel cylinder hone. Seen that cure a LOT of issues even with the cheap Winchester Universals.

I have my 835 set up for Turkeys and Deer...different barrels obviously and I've fired 2-3/4", 3", and 3-1/2" with no problems at all. Are you noticing problems with a particular brand of ammo or all ammo? My 835 has never failed to eject a round and I've tested all the popular brands to find what works best in my gun for accuracy, but have never had a failure to eject on any of them.