I uploaded a world with a few datapacks on the realm and a .json file of one of the datapacks dissapeared on upload. I retried a few times but it kept happening so I figured it would probably a problem on Mojang's side.
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This should be fixed now, see REALMS-1805
Update: Actually just found out it didn't happen to only one file out of all of them, it appears several file (seemingly random ones) have dissapeared in several datapack during the upload