Weird Glitch when my friend joins the world.

So, earlier today when my friend and I were playing, he died from fall damage and we decided to end our play session, and he didn't respawn before logging out. Then we just started to play today, and he tried logging in, so far we have tried restarting the server, his minecraft, and even resetting his internet connection, but when he joins, he falls through the world, yet can still access chat. I tried teleporting him to me, and all that comes to me is a lifeless body. Then after a while of falling, it says that he died. Then when he tries respawning, it kicks him out. How do I fix this? Any tips would be appreciated.