Rage Born Mundo Cleaver is invisible

Was in a game as Lucian with a support Morgana, against a Vayne/Mundo bot lane, and at about 5 minutes in, this support Mundo's cleavers were just invisible. Like until then we could see them, and then just bam, cant see them. Caused me and my support to lose lane which lead to us loosing the game. Has this been an ongoing bug or is it recent? And when will it be fixed? Thanks a bunch