Packet handling error

[stefanember1-spec]

Version

lithium-fabric-0.15.0+mc1.21.1

Fabric Loader 0.17.0

Minecraft 1.21.1

Description

Lithium 0.15.0 causes a client crash during chunk packet decoding on Minecraft 1.21.1.

The crash occurs while handling the packet
clientbound/minecraft:level_chunk_with_light
and throws:

java.lang.IllegalArgumentException: No value with id -1

originating from LithiumHashPalette during chunk palette decoding.

Reproduction Steps

Run Fabric 1.21.1 with Lithium 0.15.0 installed.

Use modded world generation.

Join or load a world.

Client crashes either:

before finishing world load, or

after exploring for a few seconds, depending on biome/chunk generated.

The crash is biome/chunk dependent.

I am using 35 worldgenarating/altering mods however when the following mods are removed the issue is fixed/disappears:

DistantHorizons-2.4.5-b-1.21.1-fabric-neoforge

tectonic-fabric-1.21.1-2.4.3

Terralith_1.21.x_v2.5.8

Lithium 0.15.0

Even enabling only one of these mods causes the crash.

Crash Report:

disconnect-2026-01-12_14.49.48-client.txt

[2No2Name]

Try to add the line mixin.chunk.no_locking=false to lithium.properties in the config folder.

From https://github.com/CaffeineMC/lithium/blob/1.21.1/lithium-fabric-mixin-config.md

[t-lessy]

Have the same problem, but even with the option in config. But have no DH, only structure mods and datapacks.

Also have ViaVersion stack (ViaV+ViaBackwards+ViaFabric), if this would be relatable. It works on newer versions, but not on <= server version. So, could it be conflict in different Minecraft version registries?

On server there is only the "Disconnected" message. Other log lines are same.

Lithium is on 0.15.2+mc1.21.1 version.

Uploaded logs:

disconnectlog-client.txt

latest.log

Via Dump