Karnak special counter not working

Justice_Team_3

Karnak's kit specifically sates that when you intercept, counter a heavy, or counter a special attack with a heavy, it will not cost a focus charge to place a vulnerability on the opponent. But throughout my gameplay with him, I have not been able to get the special counter mechanic to work. Even when opponents are obviously recovering from a special. This inhibits his gameplay capabilities, and his gameplay is exponentially less smooth without it. He is an amazing character that I would rank up if it were not for this character breaking bug. Does anybody else have this problem?