In game Rengar empowered E bug

I recently played a ranked game with . I was casually going in for a gank bot lane. Ulted in, stacked up, spammed E.... "Wait, what's going on" I thought to myself. "Why aren't I giving my kitty ebola? Turns out, my empowered E was on cool down. Not sure why this happened, but the hunt went terribly south.

It would be much appreciated if you guys could look into this.

Thanks.