My MPI - KM East German AK build on a Armory USA receiver sticks at the very rear of the cycle. This isn't the trigger hump but when the bolt is all the way to the rear. It doesn't do it at all when firing. This gun is super accurate and boringly reliable. But when you pull the bolt all the way to the rear it sticks then I simply push on the charging handle and it goes forward.  Is this likely a receiver issue or do you think the piston may be getting caught? I can use a buffer and eliminate the issue but I would rather fix it. Anybody got experience with this type of issue?
Aaron

Seems to be the charging handle rubbing on the top cover.