[Gameplay] Fizz E can't be cast

I was playing a ranked game and at two points in the game, the first part of the Fizz E was uncastable. It happened twice during the game, but I have not been able to reproduce it. The skill button was greyed out as though the skill hadn't been leveled, and when I pressed E or clicked on the skill button, it made the same sound as though the skill hadn't been leveled. Reconnecting to the game did not fix the bug, but after a few seconds of combat the skill was castable again.