I created a new world in creative and placed end portal frames to go to the end. I also set the world border to be 10 blocks across (using /worldborder set 10 1) which led me to spawn outside the world border when I went through the end portal. When I arrived in the end, I noticed MC-54675 and that all of the endermen outside the world border were constantly teleporting all over the place. If I set the world border to 250, they stop teleporting constantly. This was done in single player mode but I would guess that if this was done on a server with not a lot of power, it could generate lag