Lux E skill not useable even with points put in

Lux's E skill became greyed out randomly during the game. It was working fine for the first 7-8 minutes or so and then randomly stopped working. When pressed it said the skill cannot be used right now and the mana cost was set to 0 on the tooltip for some reason. I tried changing keybindings and restarting client and neither of those fixed the issue.

Lost a game and promo's based off a buggy, poorly coded game. This game is supposed to be viewed as a sport? What a joke.