HUGE Vi Gameplay Bug...Resulted in gank failure!!!

[HUGE NOTE]: Turn off sound of video before playing, the league client messed up the audio with the whole clips bug, so you will hear loud screeching noises.

Anyways, I've never experienced a gameplay bug in League and i've been playing since season 3. This is my first bug and it happened in my first promos to plat (of course). Pretty much, I took a Thresh lantern and he flashed, extending the range of the lantern (i think). Then, I used my Q to dash onto the enemy Brand. After using it showed the animation but I didn't dash, and I went no where. The skill went on cooldown and I was unable to recast it. FIX RIOT