I tried to /tp to high coordinates in the End, but I just saw a void, so I did a little experiment and I found out that the terrain is generating in stripes. So what does that mean? It means that beyond 370720, the terrain is cut off(the terrain is just a void and the biome says End Barrens), after a several thousands,maybe even ten thousands of blocks the terrain generates again, after that there is just a void and so on till the worldborder.