Chunky pre-generation breaks mob spawns and empties villages: it's the border, not the plugin

What the symptom looks like

An admin runs Chunky to pre generate a large radius so players never trigger live chunk generation, which is normally good practice. Afterward, villages stand empty. Mob farms stay silent. Structures that should be full of hostile or passive mobs sit vacant. One report on Chunky's own CurseForge page put it bluntly: "Major issue. Using this completely bricks NPC spawns. Completely empty villages, dragon hordes, dragon caves, wizard buildings, etc." It reads like the plugin broke spawning across the whole map, and the buildings being intact but lifeless makes it look worse, not better.

The actual cause

Chunky's own FAQ addresses this exact symptom by name. It is normally caused by setting the world border for the world, or the max-world-size setting in server.properties, to something smaller than the radius selected for pre generation. Mobs do not spawn outside the world border. Chunky did exactly what it was asked to do. The problem is that two separate settings, the pre generation radius and the border, were never checked against each other.

Why it happens

Terrain and structure blocks are not gated by the world border. Chunky can walk a radius of chunks far past a narrow border and generate real, complete terrain there, buildings included. Entity placement is different. Minecraft checks whether a position is inside the current world border before it will place an entity there, and that check applies to more than the natural spawn tick that fills the world with mobs over time. It also applies to the one time population step that runs when a village or other structure first generates, the step that is supposed to seed it with villagers and other starting mobs.

So a border, or a max-world-size ceiling, that is smaller than the pre generation radius produces terrain that exists but was never eligible for entity placement at the moment it generated. The village gets built. Nothing is ever placed inside it, then or later, because the one time step that would have populated it already ran and failed the border check. max-world-size causes the identical outcome through a different setting: it is a hard limit set once in server.properties that needs a restart to change, rather than a border you can move live, but generation and entity placement past it are blocked the same way.

How to tell if this is your problem

Check both settings against the radius you actually used:

/worldborder get

This reports a diameter, not a radius, so divide by two before comparing it to the number you typed into your Chunky task. Then check server.properties for max-world-size. Its default is enormous and rarely the cause unless someone lowered it deliberately, but a smaller value there produces the same symptom as a narrow border.

If either number is smaller than your pre generation radius, that is the cause. No further diagnosis needed, and nothing about Chunky's own logs or config will show it, since from Chunky's side it generated exactly the chunks it was told to.

The fix

Before running a pre generation task, set the border and max-world-size to match or exceed the radius you are about to generate, not the other way around. Do this first:

/worldborder set 20000

for a border that will cover a 10,000 block radius in every direction, then start the Chunky task.

If it has already happened, there are two ways back. The clean one is restoring from a backup taken before the original pre generation run, then redoing it correctly, which is the reason to always back up before a large operation like this. The other is expanding the border to the correct size, deleting the region files for the affected outer area, and pre generating that ring again now that the border will actually let mobs spawn there. Moving the border alone does not fix already generated chunks: the game will not revisit them or rerun their population step on its own, so the empty villages stay empty until those chunks are regenerated from scratch.

This same rule, get the border right before generation rather than after, comes up in fixing server lag and the RAM guide for a different reason: pre generating without a border at all is unbounded disk and memory growth. The border is not just a gameplay boundary. It decides how far generation, and everything the game places inside it, is allowed to go.