[GAMEPLAY]Lux could not cast her E in ARAM

I just had a game with Lux in ARAM. Occasionally when I cast my E to poke (the location it should have landed should be around the outermost turret for the purple side), the Singularity disappeared, the icon of Lucent Singularity turned gray for the whole game left and surely I could not cast it anymore in the game, while other spells were not affected. I could not tell what was the reason account for that as I realized the situation few seconds after it happened. The URL for the game (hope this may help you to track back for any details) http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1946421797/45259508