Vel'koz ult not ulting

My friend Wolfpaw8 was just in a team builder with me and from around the 25 minute mark until the end of the game his ult would not go off. He was not lagging and everything else was working fine. The sound would go off when he hit R but nothing else would happen, also the sound only happened on his end. He tried rebinding the keys and toggling quick cast but nothing worked.