Whole lot of oof in there. What happens if Driver is valid? If driver pawn is null, set view will not process.
The function should start off with a sequence node.
Then 0: get all your main references set and valid. Controller, Vehicle, Pawn etc.
Then 1: disable collision/movement, Attach, Possess.
Then 2: set view target with blend
Then 3: return
Oh an as a side note you should do all your possession from within the Game Mode.