Volibear frenzy doesn't reduce cooldown when biting a monster [GAMEPLAY]

I was playing as volibear in the jungle and when I had three stacks of frenzy(w) I activated it on red buff. the cool down was not reduced, the same thing occurred four or five more times during the game (at raptors, gromp, and wolves). it worked correctly later but those first couple of clears the cool down was not reduced.