Caitlyn autoattack bug (gameplay)

I played headhunter caitlyn in a 5v5 teambuilder. During the game sometimes her autoattack seemed to do no damage on minions and sometimes the minion died before the bullet hit the minion. I had the feeling that even when it looked like the minion didnt get damage it actually did but just didn't show. I didn't notice this effect on players. This went on al game long. I have not tried it in another game yet, so it could be a one-time weird bug.