TPA Mundo Invisible Cleaver Bug (Visual)

I was in a game as Rammus, and the enemy had a Mundo with the TPA skin. He was top and took smite/TP. At some point during the game I realized that his cleavers were entirely invisible. And it was like that for all 55 minutes of the game. As far as I could tell the Quinn on my team also couldn't see the cleavers. They didn't seem to have any irregular hit-boxes or cooldown. I do not know if the Mundo couldn't see them. I assume he could. Being that he didn't say anything about it when we did. That's really all the information I can give, I doubt anything else is relevant.