On the bottom of the slide there is a little button if you are pressing that when your are cycling the slide it will not feed the next round from the mag tube.
Mine does the same. I know that the bolt is spring loaded in the carrier so one the bolt is closed it pushes the carrier back slightly and the fore arm is connected to the carrier. It should not be an issue... I have several hundred rounds through mine and over a hundred 3 1/2 mags.
It will do that because the bolt is pushing against the barrel. It doesn't mean there is a problem, but installing it is easier with the action pulled back slightly.
The gun has a Briley Breach Buster, Nordic components +3 mag extension with low drag follower and spring, Mesa Tactical receiver mount sureshell shotshell carrier, Mesa Tactical barrel-mag clamp, Surefire scout light and a Benelli collapsible stock.
I went to the indoor range last night and put 3 boxes of shells through her and the muzzle brake works great but I can't wait to go the the rifle range and throw some slugs out of it!