I saw an argument about this on a different forum.

it sounds like the root problem is related to the SP campaign providing MP progression. So, because apparently how many times you’ve prestiged a 1911 is a major concern, all of that requires phoning home (the olds among us may remember when this was literally UbiDRM back for SC Conviction and the like…).

From what I could tell: If you gracefully disconnect then you keep your checkpoints. If you lose connectivity, you lose your progress for the entire mission.

It sucks since there really is nothing like a CoD spectacle out there. But if you just want a good FPS campaign with some fun moments? Get your Steam on.