Question: I started up Campaign in Call of Duty: Black Ops III and my progress is gone. What happened?
Answer: The single player Campaign in Call of Duty: Black Ops III has two different save files: one when playing online and one when playing offline.
Be sure that you are returning to Campaign mode in the same manner that you starting playing. If you start Campaign and do not see your progress, you may need to restart your game and enter Campaign mode in an offline or online state, depending on how you started playing.