Quest NPCs won't initiate conversation.

[ThePopeKYA]

Probably the worst bug I've seen in Skyrim as it has broken every major quest line in the game. There are moments during these quest lines where two NPCs need to talk to one another or the NPC needs to move around so this all plays out outside the dialogue box. However, when that scene ends they are supposed to then initiate dialogue with the player nothing happens. For example, I wanted to join the thieves guild. Everything goes alright until we get to the part where we meet Mercer for the first time. He successfully speaks with Brynjolf but when he's supposed to ask "Do I make myself clear?" with a dialogue box, nothing happens. He just stands there. When I activate him it just says he's busy. I've tried turning off mods, but nothing seems to be fixing this. Advice?