Invisible Baron [Gameplay]

In a Normal (draft) game recently, we were having a super intense game and the other team was trying to Baron while half my team was dead. The Rek'sai burrowed into Baron and was receiving damage from the Baron but none of us could see it or target it. This remained the case through the rest of the game. I'm not certain Baron ever appeared because no one saw it all game, although I believe there was a rift herald completed in the early stages. I will recheck the game and see if that was the case.

I'm not sure there are "steps" to reproduce this bug because it was the most random thing ever and has never happened to me before. Will update if it is a repeat occurrence.