I have had two bugs recently. Nothing huge, but caused my death more than once.

I recently played a game as Singed, where his E was messing up. I was playing against a Renekton, and when I tried to use my E to fling him into tower, it bugged out, I froze, and got stuck in the wall, leaving Renekton to kill me while I was unable to do anything. The rest of the game, my E kept bugging out, causing Singed to freeze for a few frames and delaying the activation of his ability, causing several teamfights and escapes to end in my early death.

Another issue I have had lately is with Karma and her E. Every time I cast it one someone else, it works perfectly. But when I cast it on myself, it only works about 20% of the time, and I have to recast it if I have time, or just die.