This started recently where all Xbox One X players CANNOT connect to my world but, all Original Xbox One owners CAN connect. I confirmed this because 3 players on Originals join just fine. But, then 2 others who on X's cannot.

I am on an Original.

On the other hand, when Xbox One X's host a world everybody can join. Both Orginal and X's.

I am sure this is the reason and not a network problem. Because all of us connected to each other just fine recently regardless of console.