I cannot communicate via chat

I play Minecraft with my friends. It is not a Realm, only via Xbox Live and LAN. Since May we have a problem with the In-game chat. My brother and me can communicate via chat without any problem but we play via LAN. When I write to my friend, he do not receive the message. He joins to my world via Xbox Live. It is weird because I can read his messages. He also use an Android phone.

The language that is used in the pictures is German, I hope it is no problem. The first screenshot, where you can only see "hallo" ist from the smartphone from my friend ( it is in the background. In the front there are the options). The other screenshot, where you can see a longer dialogue, is from my phone. It is the same chatroom but my friend do not receive any message.

I hope you can find a solution for this problem.