Friend must restart Minecraft every time for me to be able to join

I have made this ticket private because the video shows the usernames for myself and my son. It is Unlisted on YouTube, so only people with the link can view it.

I am on Windows 10, and he is on Xbox One.

Sometimes, when he is playing he appears on my "Friends" tab under "Joinable Friends," as he should. If I join and play, then we end the session (such as if he exits the world and goes into another, or one of us is disconnected), he will no longer appear in my Friends tab.

He will also be unable to invite me by going to "Invite to Game" while in a world. I do not appear under Online Friends. However, he appears there to me.

This video demonstrates that he is online and playing in a Minecraft world. Multiplayer is enabled in that world. All of his Xbox privacy and safety settings are set to Allow, as are mine. NAT type is set to open for both devices.

https://www.youtube.com/watch?v=3eNYy-Gy5dA

If he completely exits Minecraft and terminates the application, then restarts it, the issue is resolved, but only for one play session. When I do the same, it has no effect.