Vi Q bug (Gameplay)

During the game, I was unable to use my Q (Vault Breaker) on Vi. It only appeared towards the end of the game during a fight near baron. It might have been because when i was charging my Q, Pantheon stunned me with his W therefore cancelling the Q. However this is only speculation as I'm not sure why it happened. Nevertheless, for the last 2/3 minutes of the game I could not use my Q at all, either smartcasting or clicking on the Q with my mouse.