He's probably taking some scent blockers right?? That's why he can't smell his pheromones?...

I don't think it's the case, he seemed disappointed that koutarou didn't notice him at the party.
My delulu is telling me Koutarou is still sick and it clouded his sense of smell.

Or one of them changed medication and didn't know about potential side effects

Ooh hasn't he been taking alpha suppressants i thought so he dosnt hurt him??? Unless im misrememboring.