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

Any news for light desync?

Do you mean the nether portal lighting?

damn both
portal lights bugs most likely because of SL installed alongside with C2ME

damn both

What is the other one

I blame notickvd

Any news for light desync?

Do you mean the nether portal lighting?

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

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.

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

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

The original post was about desync that goes away on chunk reload. I blame C2ME on that

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

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

1.21.1

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

Sure, here ya go

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

w1.zip

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.

All lighting works fine for me on both 25w31a, 1.21.8 and 1.21.1. Cannot reproduce any of the issues.

Does disabling notickvd fixes all the issue you have seen?

Well it doesn't fix the light engine failure obv, but overall i don't see any desyncs so far.

Does it still happen if you enable ensureChunkCorrectness in the config?

Yes

Also please join our discord server shown in the mod page for more efficient communication.

"Unable to accept invite"

Have you reported the lighting engine bug to mojangs bug tracker? If you did, please provide a link to the report.

Also try this build with notickvd on and see if the desync still happens.

It took 1 minute

Does it still happen if you enable ensureChunkCorrectness in the config?

Also please join our discord server shown in the mod page for more efficient communication.

Try this build and see if it fixes the desync.

As I currently cannot reproduce any of these, I'm trying anything in my head to probably tackle this.

https://github.com/RelativityMC/C2ME-fabric/actions/runs/16750659147

"Unable to accept invite"

The invite should be this. Please try again.

Didn't work. Don't want either.

I managed to reproduce portal lighting glitch in a very specific way. But the glitch is also present in vanilla.

is that pure c2me and just desync (not persistent quirk)?

Try this build and see if it fixes the desync.

As I currently cannot reproduce any of these, I'm trying anything in my head to probably tackle this.

https://github.com/RelativityMC/C2ME-fabric/actions/runs/16750659147

Doesn't work.

I managed to reproduce portal lighting glitch in a very specific way. But the glitch is also present in vanilla.

is that pure c2me and just desync (not persistent quirk)?

It is vanilla. No c2me, and not even fabric-loader. It is just desync.

I managed to reproduce portal lighting glitch in a very specific way. But the glitch is also present in vanilla.

AHH, i got the rendering engine bug (probably sodium) that goes away with F3+A and i didn't screenshoted it

I managed to reproduce portal lighting glitch in a very specific way. But the glitch is also present in vanilla.

is that pure c2me and just desync (not persistent quirk)?

It is vanilla. No c2me, and not even fabric-loader. It is just desync.

F3+A first, chunk reloading second, that way we can tell it is desync or not.

Submitted to mojangs bug tracker: Nether portal lighting desync in some circumstances

https://bugs.mojang.com/browse/MC-300691

Nice battle station you've got.

Do you still keep portal and movement desync as separate issues?

In regards of portals, i was not able to reproduce it when not doing it near the world borders

I'm unable to reproduce any desync when flying around, only the portal ones that I can think of.

Can you provide a video or screenshot where the desync happens?

I would say it is the same problem as MC-300691

Basically this happens:

• Block is updated, or new neighbor is generated
• Light update is triggered and scheduled asynchronously
• A good amount of chunks get sent to the client, with old lighting data
• Light update finishes on the server, but only lighting on the edge chunks are sent
• Client lighting is now outdated

This isn't anything trivial to solve, as there is zero synchronization in vanilla minecraft. notickvd basically just amplified the issue.