The End generation is broken at long distances since 18w46a.
The terrain stops generating and then generates again from a certain distance from the center of the End.
This donut-shaped pattern repeats over and over to the edge of the world on a regular basis, starting at 370,720 blocks from the center of the End.
Use the following command to teleport to the End:
The code is trying to process numbers that are much larger than what Minecraft is actually capable of for its world terrain noise which causes part of the terrain noise to generate numbers that ultimatly get read as NaN (Not a Number) and causes the terrain generation to fail outright.
Here is the source that I used to write this ticket (examples, code analysis, visualization of what's going on...): https://youtu.be/91Feq0dHw28
Video by AntVenom.