Finite outer islands in the Minecraft End?

I am playing on a public server with a giant map.

After travelling a huge distance in the End and passing thousands of islands, suddenly there are no more islands. I guess I am at the edge of the outer-islands-donut.

What is the algorithm to determine at which coordinates the outer islands stop generating?

According to https://minecraft.gamepedia.com/The_End#Outer_islands

These outer islands generate infinitely‌

If so, why am I travelling through nothing but void space?

Update: I haven't seen any island in the last 20 000 blocks and im still going. I doubt any islands have been removed by worldedit or even by hand. I assume they do not generate infinitely. I don't know which version of MC has been used to generate the map I'm on.

This is due to a terrain generation bug in Minecraft, which is at the time of writing still unresolved. The relevant bug report can be found on the Mojang bugtracker: https://bugs.mojang.com/browse/MC-159283