This bug has existed for a long time. When a player joins a server, he/she starts slowly falling through the world and fake chunks into the void and when the world loads, the player gets teleported into the spawnpoint. it can also happen in singleplayer worlds (picture with the world border) When it happens, it looks like this:  !image-2018-10-21-14-34-20-689.png!!image-2018-10-21-14-33-46-924.png!!2018-10-03_20.04.04.png!