Pfff…Sorry man, there can be a thousand things wrong…You should try debugging and see how/where the code goes, frame by frame, (in case you never done this before, read a little bit about it here: Blueprint Debugging | Unreal Engine Documentation).
Otherwise, it could be anything: lack of a player start configured properly, initialization of camera (your prtscr looks pretty much like you are there, but just lost your camera initialization), or even the engine’s initialization sequence of actors which can cause breaking of references. In some cases, your Controller gets “spawned” after some/most of the actors, and it differs from editor to cooked build, which may get nasty.
Anyway, I’d suggest you debug your code and maybe you figure something out, see where things break, and start addressing problems from there.
Good luck! 