I just started having this issue in the last 2 days. Initially minecraft would work on sons ipad and he could log into worlds but I could not join any of his realms. We both ended up uninstalling and reinstalling minecraft, yesterday he could create a world but I could not join. When he left the world he couldn't get back into any of them - it crashed every time. Then after trying to logon to his xbox account he couldn't get into anything. It either crashes on load on the white screen, or it crashes after running for a minute or two. Minecraft will run on my ipad, but I cant join any other players.
Would like an update we have the same issue and my kids are getting quite upset about it. Can play offline but it doesn’t save their world so really frustrating.