MC-300691: lighting desyncs

[Helsium738]

Describe the bug
I've got light glitch

To Reproduce
Steps to reproduce the behavior:
Just played randomly.

Expected behavior
No bugs.

Screenshots

Runtime info (please complete the following information):

• OS: Windows 11
• Minecraft version: 25w31a
• Mod version: 0.3.5+alpha.0.10+25w31a
• Mod branch: (fill this if you are not using the default ver branches)

Crash reports / logs

https://pastebin.com/aG2sNZah

Other mods

Fabric API

Checklist

• [x ] I am using the official version of the mod.
• [ x] I tried the latest development version but the issue persists.
• [ x] I searched for similar open issues and could not find an existing bug report on this.

Additional context

[ishland]

Cannot reproduce. Do you mind providing your world? Or just seed and the exact location.

[Helsium738]

Whoa, i took a screenshot and quit yesterday and now it is gone.

[Helsium738]

1.21.1

[ishland]

Please provide logs, and crash report by holding f3+c, and the world.

[Helsium738]

Sure, here ya go

latest.log
crash-2025-08-04_12.57.33-client.txt

w1.zip

[ishland]

Still cannot reproduce your issue on both 25w31a and 1.21.1. Even with some automated checking, I still cannot get a single detection of such issue.

The way the world is broken is very unique and likely points to a lighting engine failure rather than C2ME failing to save the lighting data.

And this is the first case for lighting issues in 1.21.1+ on builds that exists on modrinth and curseforge without any other mods. I personally never encountered any of these issues on several production servers, which include heavily modded ones. Also nobody else have reported such issue before.

I would suggest trying the following things:

Try reproduce in vanilla.
If vanilla works fine, try reproduce with a normal openjdk (like azul zulu or adoptium temurin) rather than the one from microsoft.
Try disabling asyncSerialization in the config file.
And try reproduce with stock settings if you have overclocked your system like cpu or ram.
Also if you have access to another machine, try reproducing on another machine.

Take your time and please report back results.

[Helsium738]

managed to found one with openjdk from oracle and asyncSerialisation disabled, it was tough, ngl

[Helsium738]

Alright, vanilla 1.21.1 light engine is trivial to explode, you just fly in spectator very fast for 2 minutes and go back for the quirks.

[ishland]

if it does happen in vanilla, file a bug report at minecraft bug tracker.

[Helsium738]

Any news for light desync? I get 3 quirks on average every 10 minutes.

[Helsium738]

I blame notickvd

[ishland]

Any news for light desync?

Do you mean the nether portal lighting?