[MCPE-189996] Updating the world causes some loaded unchanged chunks to regenerate incorrectly

Updated by @unknown.
Summary:
Updating the world causes some loaded unchanged chunks to regenerate incorrectly.
As a result, cut-off water appears in caves, air under water, the landscape on the surface changes, etc.
This does not affect newly created worlds and chunks that were not previously generated.

Steps to reproduce:

Create a world in 1.21.51 with seed -3763674536482985406.
Teleport to coordinates -14 63 -17.
Save the world.
Update to version 1.21.60.
Open the created world.

Observed results:
The generation of the world around you is broken.

Expected results:
The generation will correspond to the current seed, as a result of which there will be no corrupted chunks.

Original description:
Many parts of rivers are broken in the latest Preview version. I have exported a world from the non-preview version of the game (1.21.51) to the preview version, and when I opened the world, I saw that many river chunks are broken, being overwritten with land instead. It seems like it doesn't overwrite caves, only the water.

I attached some screenshots of 2 different coordinates in the same world in both the non-preview and preview versions showing how the chunks in the Preview are broken in rivers.

Linked issues

is duplicated by 24

MCPE-155333 Aquifer chunk found generating in normal cave Resolved

MCPE-171609 Weird patches of grass and air pocket spawn underwater Resolved

MCPE-175571 Unusual boxy translucent structural outline on ocean floor? Resolved

MCPE-175706 Chunks get replaced/Reset and have odd generation Resolved

MCPE-189165 Problem with the water Resolved

19 more links

relates to 1

MCPE-175332 Discontinuity between chunks generated in 1.20.30 and 1.20.15, where terrain blending should not be necessary Resolved

Attachments

Backup 6.mcworld

Minecraft 25-04-25 10_46_37-20250425-084638.png

Minecraft 25-04-25 14_24_13-20250425-122414.png

Minecraft Preview 1_21_2025 8_13_18 PM.png

Minecraft Preview 1_21_2025 8_15_43 PM.png

Comments 18

[Mod] EVGENSYPERPRO 2025-01-22T09:01:13Z

1.21.60.27 (new world)

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1.21.60.27 (updated from 1.21.51)

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1.21.51

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Odyssey 2025-02-10T05:20:30Z

Still in 1.21.70.22

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Meme Thius 2025-03-11T00:37:24Z

Ive had these same issues and it is really weird. I hope they fix this bug quickly

Meme Thius 2025-03-11T00:40:57Z

Also, btw, this issue happened to me in a different seed too, so the inclusion of the seed seems irrelevant and it seems like this is a broaded bug. Here are some images of this bug in my world

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Yuu2519 2025-03-29T05:37:56Z

This issue also happens in 1.21.70.

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8 more comments

voyager 2025-04-03T16:31:09Z

The same problem ((((
This broke my world in the realm where we had been playing with my children for a year and a half 😢

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Flipy027 2025-04-17T01:08:02Z

Still a huge Problem :(

Loïc Dubar 2025-04-25T12:31:30Z

I can confirm (I accidentally made a duplicate) but to clarify, the chunks that regenerate incorrectly are the ones that the game never saved. From my experience, it seems like the game thinks that the old loaded chunks are frozen plains and try to blend them in with the iceberg biome.

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FIX (maybe)

One fix for this, if you have a backup from before reloading the area, is to use https://www.chunker.app/ to update the world version, the conversion process make it so the game thinks the old loaded chunks are from the current version so it doesn’t try to incorrectly blend them in (my theory). It also works if the backup was opened in the newer version but the problematic area wasn’t visited (in this case, you just force the update of the chunks with the tool before the game does). Unfortunately, it might also break a necessary blend somewhere else (where there would be a new biome) if you can’t load that area before but I cannot verify that (my biomes haven’t changed in the loaded part of my world).

It worked for me:

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After that, you should probably make sure to load ALL the chunks of the area before the next update.

voyager 2025-04-25T18:17:21Z

Its an interesting idea. But how can I do this for realm?
I don't worry so much about other worlds. Only about the world in the realm where I've been playing with my kids for a long time. And it's terrible what happened there with the frozen oceans :(((

jennaw3 2025-05-02T23:44:48Z

This affects trees too and isn’t limited to cold biomes, as shown by these before and after map screenshots.

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SugarKingMC 2025-06-17T14:36:43Z

Same here my world is also affected with that bug and i'm on version 1.21.82

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et1et 2025-06-17T22:48:29Z

This is a really horrible bug that really needs to be fixed. And it should be pretty trivial to fix based off of what Loic discovered.

GoldenHelmet 2025-06-18T14:00:02Z

Loïc: thank you for the information. Are you saying that when the game generates chunks and checks whether neighboring chunks have been generated in a previous version, it then fails to compute the biome correctly for the chunk it is generating? Or is it failing to read the biome data of the previously saved chunk, so that the blending in the new chunk assumes a default biome for the (seed-computed) temperature?

Note: this sounds like the same underlying mechanism as MCPE-175332.

et1et 2025-06-20T22:59:51Z

No, what Loic is saying is that, if when the game updates to a new version, minecraft were to mark all chunks as generated in the new version before loading the game, this problem may go away. That would be a pretty trivial fix.

SugarKingMC 2025-06-24T18:32:46Z

The desert is also affected with that bug and the game things desert is lush biome

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blab blob 2025-07-11T19:19:07Z

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Having similar issues and it’s incredibly frustrating, is there any way to fix it yet?

Nreed002 2025-07-19T00:33:20Z

Nope, it sucks and I don’t think they’ll be fixing it anytime soon. This has been an issue for a while I feel like.

Loïc Dubar 2025-07-20T21:47:40Z

GoldenHelmet: I am saying that when the game generates chunks and checks whether neighboring chunks have been generated in a previous version, it then misinterprets the biome data of the previously saved chunk (or fails and assume a default). Then, there is a wrong blending in the new chunk causing the discontinuities.

And no, it doesn’t seems to be exactly the same underlying mechanism as MCPE-175332 since it seems to be missing the blending (the biomes seems to be unchanged in the screenshots) rather than blending with the wrong biome.

Also, I don’t really agree with the description of this bug and I opened MCPE-217769 which was closed as a duplicate. Sorry for the delayed response, I hadn’t enabled the notifications.

et1et got the idea of the way I fixed the issue for my world. It only works since the biomes in that area of the world didn’t change between the versions.

blab blob: Have you read my previous comment? It has the description of my fix.

P.S. THE BUG ISN’T FIXED YET! (opening the game with my backups still cause the bug). I would still like to see this bug fixed so I can enjoy opening my old backups again. Here is one of them if it can help (1.21.5* according to https://www.chunker.app/ ):

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