/viaversion dump Output

https://dump.viaversion.com/125266f696876f238baeeaac43536d4cb711952c2330653b2253b3daedc3a2dd

Console Error

Internal Exception: io.netty.handler.codec.DecoderException: Failed to decode packet 'clientbound/minecraft:container_set_content'

Bug Description

When users under the ViaBackwards protocol, like 1.21.4, when the server is on 1.21.5, they are kicked under that error message.

Steps to Reproduce

1. Attempt to Login with a client under older version (e.g. 1.21.4)

Expected Behavior

Player should be able to login without error

Additional Server Info

I use a handful of mods, but have not had issues up until this random point. It was a recent switch to 1.21.5, as Geyser needed it to support the latest version, but noticing how the error is ViaBackwards related, I'm unsure of the main cause. After initially making this report, I switched to the latest ViaBackwards build, and it caused the issue detailed above. Before however, I had an error which specifically mentioned ViaBackwards.rewrite.api or something similar when a player interacted with a chest slot, kicking them instantly; Though, that was on 5.3.2 of ViaBackwards, now I'm on 5.3.3-SNAPSHOT.

Checklist

• I have checked if this is specific to ViaFabric platform, and doesn't happen when running it on other platforms (Paper/Sponge/Velocity/Waterfall).
• I have included a ViaVersion dump.
• If applicable, I have included a paste (not a screenshot) of the error.
• I have tried the latest build(s) from https://ci.viaversion.com/ and the issue still persists.

Can you test your server with Fabric API and ViaFabric+ViaVersion+ViaBackwards only? this sounds like it was caused by a third-party mod sending bad container content changes.

Closing this issue in favor of this.