Oh hey it happened to me too with that mask (and it was a new set, just like yours)!
it's a factory error or something, and I never bothered to buy a new one.
(also, I know, I replied to a very old post)
Other than that, my Kirop was once hit by a deadly football ball (or soccer ball, how you prefer), which caused a bit of damage to its mask. The mask itself is a bit bent, and the axle is no longer there. Instead, it is now permanently inside the AV Matoran head. If I ever find it in my bin of parts, I'll post a picture.