If you teleport exactly 524288 blocks orthogonally from the center of the map, you can see a giant clif of end stone where island generation cuts off. If you teleport out 524288/sqrt(2) blocks on both axes, you get a diagonal cliff, which proves that this phenomenon exists in a circle fashion. This is a rather new terrain generation glitch, and one which proves somewhat disruptive when attempting to explore extremes of the end far lands. So it should probably have a fix implemented in this mod.

Bug tracker ticket on this issue: https://bugs.mojang.com/browse/MC-159283

closing as the notice on this mod's readme has announced discontinuation for a while now - feel free to reopen in future if work starts again

Fixing this for netherhigher may also be a good idea.