Sometimes when I make a new follower, they don't give me the follower dialouge. They'll say stuff like "Need something?", "Huh?", or "Make it quick.", but never the follower dialouge, making it impossible to get them to follow me. I go to their factions tab and make sure that CurrentFollowerFaction is set to -1, and PotentialFollowerFaction stays as it is. Then I go to Characters -> Relationships, make sure they're set as the Parent NPC and the Player is the Child NPC, and that the relationship is set to Ally. I double check all of this, and then double check to make sure the .esp file is active, and they still don't give me the correct follower dialogue. What gives?

Have you checked the voice types? Not all can be used as followers.