My friend was AFK in my world 2 days ago and his Xbox turned off. Since then, he can no longer join that particular world.

Instead he gets stuck on "Locating Server" on his screen, while I can see his character in my world the character is invincible and unmovable.

He CAN load onto a different world of mine, and I CAN load into his world. 

How do I fix this so my friend can join my multiple hundred hour world without me feeling like I need to throw it all in the trash because it's bugged?

We have tried the following:

• Checked NAT type (both Open)
• Hard reset Xbox (hold button on front, both of us)
• Deleting cache in MC menu (both)
• Uninstalling and reinstalling Minecraft (both)
• Same as last, but this time I copy the world once before loading it
• Tested joining a different world of mine: works
• Tested joining his world: works
• My wife's account can still connect to this world, and his.

When I searched on this topic I found something about iOs but no solutions? I couldn't follow the post and I didn't seem like it was for Xbox One, so here I am, sorry if this is a duplicate... if it is, maybe there is already a workaround... ?