I also have this issue occurring on Win10 Edition. My realm is only ~280mb, but I also have the VanillaBDCraft textures someone else mentioned and I'm assuming that's the culprit. Issue is, i can't remove the texture pack if I can't download the world first. So did I just pay $5 for a texture pack just to break my realm?
What's the point of this website? It seems like the vast majority of bug reports are ignored.
I am also having this issue. I can no longer add or remove texture packs on my realm because I get a "some of the selected content could not be applied" error.