Chokes can split if they start to back out slightly, and plastic and fouling builds up under the skirt. When enough fouling gets between the choke and the barrel to lift a the skirt into the bore, it can catch the wad, as this one did. Make sure your tubes are snug. Also, if you ever drop a tube, check it very carefully to be sure it’s still concentric. The steel is thin and chokes are fragile, and an out-of-round skirt can snag a wad, too. Depending on how much you spent on the tube, either toss it or have a gunsmith straighten it out for you.