So /vp/, why is my Sylveon unusable online?

Hardy
Sturdy Body
Cute Charm

Moonblast
Light Screen
Reflect
Charm

I caught it early on in the game and have just used it to throw up light screen at the beginning of a match, I don't understand why all of a sudden it's banned?? I've tried different combinations of my party and have determined it's sylveon for sure that I can't use