Well I reset the realm on my pc and RE replaced the realm with the copy i had originally downloaded and got working by deleting cloud sync files and could download it on my xbox with No issues. i had trouble the other way round (Had the world on my xbox and transfered that to the realm and transfered to pc) as xbox starting to lag badly. you could try to back them up but make sure they load correctly. I would assume your trying to do the same xbox to iOS ?.
had the same issue also on win 10 and android but found if I deleted the cloud save files which there are 2 in the world save folder it loaded straight up on both platforms.
Well I reset the realm on my pc and RE replaced the realm with the copy i had originally downloaded and got working by deleting cloud sync files and could download it on my xbox with No issues. i had trouble the other way round (Had the world on my xbox and transfered that to the realm and transfered to pc) as xbox starting to lag badly. you could try to back them up but make sure they load correctly. I would assume your trying to do the same xbox to iOS ?.