[GAMEPLAY] Untargetable Bug

Today, August 8th, I was playing a 5v5 blind pick. We were doing the final teamfight, about 45 minutes into the game, and I was about to kill the Garen with a final auto attack as Vayne. However, he was turned untargetable. This was caused by Cassiopeia's ultimate. His health bar was there, but Garen was untargetable, so it made me move into the middle of the fight because "nothing" was there. As soon as Cassiopeia's ult ended, Garen was back to normal and I did kill him before I was bursted. We lost because of that. At least it was a normals for me, but this could happen in ranked to someone. I have no clue how it happened, but I can definitely tell you that it was caused by Cassiopeia's ult.