I completed gta v story mode on Xbox 360 but when I came to Xbox one my story mode data hadn't transferred whereas my online character and level did. How do I get it back?
To sum it up: Only your online profile is transferable between old and current gen consoles. Single player saves are not.
Only your online profile can be transferred to a current gen console or PC. The single player saves can not be transferred as the current gen story mode contains lots of new elements that last gen did not. Rockstar prevents this so you don't break your save.