I cant see my friends world in friends tab in minecraft PE

When my friend joins his world , I dont see it in the friends tab.when he sends invites, i dont recieve them.I can see him online and playing minecraft on xbox app but not in minecraft.Sometimes he appeared offline in xbox app when he told me he was actually in his world.We dont play on local wifi but play online multiplayer.His world's multiplayer is on and is visible to friends.I could see his world a few days ago but now i cant see it anymore thus cant join and play with him.Please fix this bug. Thanks