Connecting to a friend's world is impossible between mobile devices but works between mobile and PC. I've created a new Microsoft (Xbox) account and tried to see if it was based on settings on Xbox Live/Minecraft and had a friend do the same. We were unable to do as little as see the other's world in the Friends list.
We did see if a fresh install would work and recieved the same resault. We went as far as opting out of the beta and verifying it was a beta issue. We were able to connect outside beta. The link with Xbox Live has been shady for the past few updates aside from this issue alone. The link with Xbox Live that ties our 5 skins has been bugging out (MC fully loaded and account is logged in. Had to manually go into Skins and reload characters.