Yeah, the connector and disconnector must be assembled properly before installing the trigger group but that wouldn't cause an intermittent. (Covered in Owner's Manual because it's easy to misalign IIRC.) I suppose I'd instinctively move the carrier out of the way to get to the follower but dunno.
Don't have one to look at so to Kuhnhausen's manual. The troubleshooting section for shotgun "does not open" covers mostly other than worked manually. So filtering...
Action bar/sleeve assembly bent, damaged (binds action)
Ejector altered, damaged, broken or broken loose
Early carrier latch release
Barrel misaligned
Hammer binds on recock (damaged hammer or hammer plunger)
Hammer binds on recock (trigger plate housing damaged)
Firing pin retaining pin loose, slipped down (pin drags, binds side block)
I'd take a close look at the carrier latch and related. Probably mainly because I fixed one once (long time ago) with a twisted latch. Being at the front of the trigger group it's likely to catch more hell than the rest of the group. Probably would check the firing pin, retaining pin and the bolt/block first because it's easy.
Hard to figure out without having it in one's hands.
