[Gameplay] Veigar Ultimate Bug

Twice when playing Veigar and I used his ultmate the animation will go off but nothing happens, the ult does not go on cooldown nor does it do anything to the enemy champion. I've found it happens when I ult and suddenly the enemy chappens goes into fog of war I watched as the ult flew but as soon as it entered the fog of war it dissappeared and nothing happened.