I encounter this when attempting to delete one or more named ranged from the defined names in the management box. It's hit or miss; some range names that I deleted several times, keep reappearing and others that I wanted to keep will be deleted. When this named ranges that I don't delete, disappear they will do it in the order which it was created. For example see my attached pic the named range that appears at the top of the list will be the next one to be disappear if it happens.