my friend recently bought a realms server and attempted to upload a world we and a few other buddies have invested quite some time into. 

at first, we couldnt connect at all, but when we could and my friend uploaded the world we had been playing on, it only created a new world with the same seed.

quote from my friend:
"When going into the settings of my world and pressing play on realm i am prompted normally to choose the realm to transfer to. Then a confirmation to wipe the old world to transfer with the new world. After confirming it, it exports it successfully. But then when it tries to initialize the upload, no loading bar appears and after a few seconds an error bubble pops up simply saying an error occurred. This also happens when trying to do it from the realm settings menu. A backup is made but does not properly transfer the world, only the world seed."