MCPE crashes after being open for a few minutes + Can't invite friends

Hello Mojang,

One day I opened MCPE on my IOS 11.4 iPad Pro to play with my friend. I clicked into a world and went to invite her and the message "Oops! You were disconnected from your xbox live account, reopen your world to invite players." I reopened the world, it stayed with the same message. I then reopened the world again and it didnt changed. I cleared the tab and it still had the same message. I then restarted my iPad Pro and nothing changed. I then deleted minecraft and redownload it, nothing changed. How do I fix this?