If the hammer won’t rotate back off the case head when you drop the lever, the firing pin will drag on the case head or plug seater. The plug will probably be worse than the cartridge because it’s jammed between the bullet and the breech face.  A fired cartridge  generally has some headspace, or it’s just the primer backed out.

It could just be that the trigger is adjusted too light, and the sear won’t engage. The sear and or hammer worn. The other thing that can happen is the cam on the link is a poor fit for and just isn’t rolling the hammer back enough. 

It’s also possible to get the link in backwards. But I don’t remember what that causes, but it’s worth a look. If it will manually hold if you pull it back halfway, I might suspect this. I tried it wondering if it would be like a 44 and go to full cock. It didn’t.