This has been a long running bug that has been occurring even before the nether update. I have upvoted every bug report containing this bug and I've tried contacting realms support. The issue is after clicking the download world option the game goes to download the world but then stalls. No matter how long the console is left on to download the world, Minecraft never gets past the stall point on the download. I've read the comment sections of all the bug reports related to this and non of the suggested work arounds work. Any information that might be valuable to rooting out this bug I'll be more than happy to provide.