With Minecraft Java, if i join an external server using Direct Connect, the momenti  land i see me falling though the world and after a while i can see the world spawning above me.

I keep falling until i get a Timed out.

The others on the server sees me standing on the block without problems.

If i then host, and others join me same way, then they fall though the world.

Tried with forge installed and without forge (clean install) and still the same.