Garen's Ult BUg

It happens once in a while when I play Garen.

The first time it happened to me was when I pressed R on Heimerdinger, and the ult did not go off. I was literally right next to him, and the ult was not on cool down.

and also just now in my ranked game, when I pressed R on Zilean in ult range, it did not do anything.