Volibear passive not activating lategame

I was playing a game of volibear, and lategame my passive would not activate. It almost cost us the game, and it took me a couple of deaths to realize that it wasn't working. After that, I sold spirit visage and changed my build, but if I hadn't have noticed, it was likely we would have lost. If there was another reason or something someone on the enemy team was building that stopped it, lemme know how much of a noob I am, but I found it really odd that my passive would not activate once I hit level 18 it seemed. Anyways, hope this gets patched up if it is indeed a bug. Thanks