Are you guys trying to access the content through the game's store front connection? I don't think it works.
I just bought Severed on the Xbox web store, along with the free online pass and multiplayer maps, and downloaded them from the games and apps section of the Xbox One. You have to select "Manage game" and download from the Ready to install section.
Yes, but the Collector's Edition content is still not available, either in the Store, or via Manage Game, it's just not been made available to download.