Vel'Koz Ultimate Bug

So yesterday I played only two games and in both games my Vel'Koz ultimate just stopped. That's all i can say is it just stopped. It's just like if it had been canceled but no one was around me to knock me up. It did it twice out of three in one game and stopped me from getting kills. Plus the cool-down timer was the same as if I had used it. I hope this gets fixed because it was bothering me, thanks