Some chunks visually not loading for the client

[Steventheperson]

Expected behavior

Expecting to see, chunks.

Observed/Actual behavior

Chunks visually missing:

Steps/models to reproduce

Fly around, find missing chunks.

Plugin and Datapack List

None

Paper version

This server is running Paper version 1.21.10-91-main@9934c17 (2025-10-27T18:27:20Z) (Implementing API version 1.21.10-R0.1-SNAPSHOT)
You are running the latest version
Previous version: 1.21.10-88-2a1871b (MC: 1.21.10)

Other

Started after this commit onwards in build 88 to current:
2a1871b

Vanilla client and modded (Lunar) one. Tried with and without shaders / fabric.
Not related to render distance as simulation is 10 and no ticked is 16.
Chunk threads are set to -1, no problems from that either.

Here is my spark report for some additional server info
https://spark.lucko.me/v4Q1f3PrcM

[exkc]

hey all i faced the same issue it seem it is desync issue of client and server

let say client render distance is 32

then when the client joined sometime the server wont give out 32 chunk

hence caused this issue

it seem setting render distance from 32 to 10 then back to 32 fixed it

so it seem it is more likey a desync issue

BTW thx

https://namemc.com/profile/HeroSuperDylan.1

https://namemc.com/profile/Sculk_Cadet.1

for lmk it is likey a desync issue

[Malfrador]

When it happens again, please run /paper debug chunks and attach the file created by that. The chunks dump is created in <server main folder>/debug/.

[rwnd-bradley]

Can confirm exact same behaviour on latest 1.21.10 commit too. After players enter a server, chunks outside of their view distance have a high chance of not visually loading, though they can still walk on and highlight these invisible blocks. Sometimes previously loaded chunks will be affected when flying away and returning.

Setting the server's view-distance in server.properties to 32 seems to be "working" as a hacky fix.

[Malfrador]

Can reproduce this, Still happening in 1.21.11 too.
Even with vd=32, I still can get to happen quite a lot. The only fix that works for me is relogging, even changing the view-distance in the client settings or via the API does not make the chunks load sadly.

Here is a chunk dump from one such occassion: https://pastes.dev/Ye1jNo3l8Z

[Malfrador]

Few more observations:

• The loading issue is visual and client-side only. The chunks have proper collisions, allow swimming and spawn mobs. I recall issues similar to this having to do with the chunk send order.
• It happens more often if the client view distance is higher than the server view distance
• Setting the client view distance to a lower value after the issue happened will at least allow you to continue loading new chunks. The chunks that originally failed to load will however never load until you relog.
• Changing the global config chunk-loading settings seem to have no effect, nor does turning off auto-config-send-distance
• Thread count does not matter, it happens both on system with just two and with 16 CPU threads. It also happens on both Windows and Linux systems.
• The client log gets spammed with the following:

[23:59:38] [Render thread/WARN]: Ignoring chunk since it's not in the view range: 173, -187
[23:59:38] [Render thread/WARN]: Ignoring chunk since it's not in the view range: 153, -179
[23:59:38] [Render thread/WARN]: Ignoring chunk since it's not in the view range: 183, -177
[23:59:38] [Render thread/WARN]: Ignoring chunk since it's not in the view range: 161, -187
[23:59:38] [Render thread/WARN]: Ignoring chunk since it's not in the view range: 171, -190
[23:59:38] [Render thread/WARN]: Ignoring chunk since it's not in the view range: 161, -188

Additionally here is a Thread dump. Not really seeing anything noticeable in there, the chunk I/O and loading threads all just seem to be waiting on work.

I can also confirm that it only happens with the changes from 2a1871b. Reverted those in my fork and so far the issue seems to be gone.

[rwnd-bradley]

I would propose that the problematic commit was temporarily reverted given how impactful this issue is to gameplay.