Client 1.21[.1] cannot enter 1.21.11 fabric server

[Kichura]

/viaversion dump Output

https://dump.viaversion.com/0917de5929867343e184fbfe7ee06386f8d8624f45553089fce744e520350bcb

Server/Client Error

The server logs can be found here.

Bug Description

When joining the 1.21.11 server with vanilla 1.21[.1] client, The client is immediately kicked with random packet error.

Steps to Reproduce

1. Use a vanilla client that has 1.21[.1],
2. Make a fabric 1.21.11 server that only has Fabric API, ViaBackwards, ViaFabric and ViaVersion installed,
3. Join the server with said client,
4. You should get kicked at this point.

Additional Server Info

1. This server is not hooked up to any proxies,
2. This server is using Fabric 0.18.4 with Java 25,
3. This server has Fabric API 0.141.3, ViaBackwards + ViaVersion 5.7.2-SNAPSHOT and ViaFabric 0.4.21+138.

Checklist

• I have checked if this is specific to ViaFabric platform, and doesn't happen when running it on other platforms (Paper/Sponge/Velocity).
• 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.

[masterblaster221]

will this be fixed soon?

[Kichura]

will this be fixed soon?

No ETA but anything high priority is to be checked first and then anything else.

[CreeperHaed]

Is the Client really Vanilla or is it Fabric with Fabric API?

[florianreuth]

Very interesting issue, no idea what this could be

[Axionize]

I am almost certain this is a ViaFabric regression problem.

GrimAnticheat/Grim#2467

If I recall correctly from my testing in w/Grim and older ViaFabric builds. 0.4.21+135 works perfectly fine but newer versions do not, provided you update the ViaVersion jar by dropping a newer via build into the mods folder overriding the included one.

[masterblaster221]

i have the issue without grim
i am on fabric client only fabric api and fabric same on server with viafabric via version plus via backwards just can't connect with viafabric and via backwards on server but it is on backend of a velocity backend velocity dose not have via fabric

[CreeperHaed]

Isn't this bug similar to #428 (comment) ?

They fixed it for the newer Fabric Server Versions, but 1.21.9 and below still has to suffer.

How I got the Bug:

Client and Server are Fabric with Fabric API
Either the Fabric Server has viaFabric or Velocity has viaVersion installed!

Client and Server both want to switch to Fabric API Packets, but viaVersion still modifies them and ends up with missmatched packet sizes. In the other Issue it was manly because of particles generated by a player falling on a ground and the Fabric Particles-API

My fix was: overwriting the Included Particle API... because that just works for some reason, but I only recommend it on Semi-Vanilla Servers (Servers, where Vanilla Clients can still join without issues)

I tested it a lot, it's always a mix of Fabric API on both sides with viaVersion on the Server/Proxy side trying to modify packets.
I mean @Kichura you could try my dumb fix: #428 (comment)

(make the Version number something high so the console won't annoy you on every server start that i doesn't like the Version)

[Kichura]

Isn't this bug similar to #428 (comment) ?

it's not, second we already have a particles workaround implemented and third i do not use windows. meaning your resolution is not helpful here.

[CreeperHaed]

Yeah ok I "kinda" mentioned that 1.21.11 has it fixed and even the Version on your side checks out, so that is my fault for not seeing it.

The Problems are just so similar in my opinion, I kinda got confused.

Just some questions:

• Is it only for Vanilla Clients? (Maybe Fabric Client with/without Fabric API gives a similar problem)
• What is the exact Packet Error you are seing?

[Kichura]

* Is it only for Vanilla Clients? (Maybe Fabric Client with/without Fabric API gives a similar problem)

* What is the exact Packet Error you are seing?

1. It is regardless of that.
2. The packet errors are always random on each connect. (i said this at beginning btw)