It always say; Unable to connect to the world when I am trying to join my friend's world.

It always says; Unable to connect to the world when I am trying to join my friend's world. My other friends can join the world. My Network connection is perfect, has enough storage to play Minecraft. I changed the account but still can not join in the world. When it said connecting to the multiplayer game, the screen freezes about 5 sec and eventually, it says Unable to connect to the world. However, it happens only for IOS, not for Android. I can not speak English well, so I apologize if I couldn't tell you about the bug well. Please fix this bug.