The Cayde's Pathfinder achievement never unlocked for me. There was an issue with the internet connection. After I received my last subclass the nightstalker class and before the mission ended I was kicked out. I thought I could go back and finish the mission but it wasn't there. Even though now I have all the subclasses the achievement didn't unlock. I'm not sure but I think the achievement is tied to finishing the mission not just unlocking the last subclass which I cannot do anymore because it isn't there.