I asked 505 for help on this, and they responded with the suggestion below. It came from another user, and it hasn't worked for me but I thought I'd post it here in case it might work for anyone on here
(1) Use Cloud character on local world. (The world was created in 11212; the Cloud character existed before that version, and is the first character in the list of cloud characters. If it matters.)
(2) Play for a while, and then use the menu to exit the world. The application may crash.
(3) Restart the application. Play -> Cloud Save
-- You will get: "iCloud is still retrieving cloud data. Please try again."
-- If you keep trying for long enough, it will give you the normal screen to choose your character, but they're all blank. The cloud-saved characters seem gone.
(4) Cancel that option, and choose a local character. Now, for the world, if you choose Start Game -> Cloud Save you'll discover that your Cloud-saved world should be here.
(5) So if you keeping going back in the menu to the character-selection screen, the "Cloud Save" option will boot up, and the cloud-saved characters should be back.