Mundo Mundo invisible cleaver

Was playing ARAM earlier and at first Mundo Mundo's cleavers were visible. Then after a few minutes of game play his cleavers went invisible. I can see people getting hit with them and damaged. Due to the blood graphics and cleaver sound. But, it's very hard to dodge a invisible cleaver. I was not the only one who could not see them. My team also confirmed they could not see the cleaver.