Dave Farrington details a problem with iCloud Drive on the Mac (which likely exists on iPhone and iPad, too, but isn’t as easy to determine). Leftover folders from removed applications.
I understand why Apple allows file and folder visibility for specific apps or user created folders, but I do not understand why those folders cannot be deleted. That’s right. Right-Click. Select Move to Trash. Click Delete. That does not delete the folder. They are orphaned.
You need a Mac utility that displays hidden files in the Finder, of course, but one look at iCloud Drive and you’ll see the orphaned folders. I can’t find a way to delete them.