If it has a vent liner, remove it and check out its length.
Its length should be the same as the thickness of the barrel wall where it is installed.
If it's length is longer than the barrel wall is thick, that would explain your hang fires.
If you can't remove the liner, either use a good flashlight to light up the inside of the bore and look down where the vent liner would be.
If you see it sticking out into the bore, its length needs to be fixed.
If the bore down at the breech is very dirty and you can't see the area where the vent liker would be, run a bore sized cleaning jag down until it stops on something.
Mark the cleaning rod at the muzzle and remove it.
Then, line up the mark with the muzzle and check out the jag's location.
It should be past the vent liner at least 1/16".