iOS cannot host game when connected to wifi

Hello everyone. I’m using UE 4.9

I’ve made a multiplayer game, packaged it for iOS and run on my iPhone.
I can host game without any problem on iOS. But when I turn on mobile data or when connected to wifi, game hosting always fail. I don’t know what to do. I’m not sure if it is a bug of UE.

If you have any solution or advice, pls help me. Thank you very much.