ARAM Bug

This bug doesn't happen often but it is incredibly noticeable when it happens.

Basically, I'll rarely get a bug on aram that simply causes my ult to not work. One game was with Vi, one was Zilean, and another was as Shen. Regardless of how many times I spammed my ult on a champion, it wouldn't go off. The Shen match I played today included a Lissandra who had the same problem. Interestingly, after about 10 minutes, it would work again.

I have no clue what causes it or how to recreate it and the only similarity I see is that it's always a targeted ultimate. I would really like to see this fixed as it is quite a game-breaker!