It can either be a defect or in some stories they can get their pheromone glands removed when they are young so that they don't develop pheromones at all once puberty comes. It's most likely the first one though
I think he’s a recessive alpha. There was something similar like that in “Do You Still Like Me?” (also alpha x alpha) I think where one of the alphas didn’t have pheromones because of that.
welp that was some bull