[1.21.11->1.20.11] Server on newer version sends ExplosionS2CPacket on entity dismount to the client

[kodalee]

'/viaversion dump' Output

https://dump.viaversion.com/b0f69b6a2fb430f9af082aa18de8ce1b018932e721d85bc4cc68eac184e7786d

Server/Client Error

No server/client error logs

Bug Description

On client version 1.20.1, connected to a server version 1.21.11, when a player dismounting from an entity, the server sends the ExplosionS2CPacket (net/minecraft/network/packet/s2c/play/ExplosionS2CPacket or net/minecraft/class_2664) to the client.

Snippet from a packet inspector

{
  "_class": "net/minecraft/network/packet/s2c/play/ExplosionS2CPacket",
  "Lnet/minecraft/network/packet/s2c/play/ExplosionS2CPacket;x:D": 0.0,
  "Lnet/minecraft/network/packet/s2c/play/ExplosionS2CPacket;y:D": 0.0,
  "Lnet/minecraft/network/packet/s2c/play/ExplosionS2CPacket;z:D": 0.0,
  "Lnet/minecraft/network/packet/s2c/play/ExplosionS2CPacket;radius:F": 0.0,
  "Lnet/minecraft/network/packet/s2c/play/ExplosionS2CPacket;affectedBlocks:Ljava/util/List;": "[]",
  "Lnet/minecraft/network/packet/s2c/play/ExplosionS2CPacket;playerVelocityX:F": 0.0,
  "Lnet/minecraft/network/packet/s2c/play/ExplosionS2CPacket;playerVelocityY:F": 0.0,
  "Lnet/minecraft/network/packet/s2c/play/ExplosionS2CPacket;playerVelocityZ:F": 0.0
}

Steps to Reproduce

1. Start a 1.21.11 server with ViaVersion and ViaBackwards installed
2. Join on the 1.20.1 client (unsure if or what other versions also have this issue)
3. Get on an entity of any sort.
4. Dismount from the entity
5. Witness an explosion at 0, 0, 0

Additional Server Info

I use Velocity 3.5.0-SNAPSHOT (git-f712997d-b593) with the following addons:

• Apollo API by Lunar Client
• bStats (builtin)
• Citadel (custom staff module, no in-game modifications)
• Litebans
• LuckPerms
• minimotd
• SignedVelocity

Paper server information:

[03:50:28 INFO]: This server is running Paper version 1.21.11-69-main@94d0c97 (2025-12-30T20:33:30Z) (Implementing API version 1.21.11-R0.1-SNAPSHOT)
You are running the latest version
[03:51:01 INFO]: SignedVelocity version 1.4.1
Allows you to cancel or modify messages or commands from Velocity without synchronization problems
Author: 4drian3d
[03:51:08 INFO]: Aether version 1.0:PRIVATE-SNAPSHOT
Website: https://github.com/ursinelabs/aether
Author: Koda
[03:51:18 INFO]: Easyspeak version 1.0
Website: https://github.com/kodalee/easyspeak
Author: Koda
[03:51:24 INFO]: FastAsyncWorldEdit version 2.15.1-SNAPSHOT-1303+a843225
Blazingly fast world manipulation for builders, large networks and developers.
Website: https://modrinth.com/plugin/fastasyncworldedit/
Authors: Empire92, MattBDev, IronApollo, dordsor21, and NotMyFault
[03:51:27 INFO]: LuckPerms version 5.5.42
A permissions plugin
Website: https://luckperms.net
Author: Luck
[03:51:30 INFO]: PlaceholderAPI version 2.12.2
An awesome placeholder provider!
Author: HelpChat
[03:51:34 INFO]: ViaBackwards version 5.9.0
Allows the connection of older clients to newer server versions for Minecraft servers.
Website: https://viaversion.com/backwards
Authors: Matsv, kennytv, Gerrygames, creeper123123321, ForceUpdate1, and EnZaXD
[03:51:37 INFO]: ViaVersion version 5.9.0
Allows the connection of newer clients to older server versions for Minecraft servers.
Website: https://viaversion.com
Authors: _MylesC, creeper123123321, Gerrygames, kennytv, Matsv, EnZaXD, and RK_01

Checklist

• Via plugins are only running on EITHER the backend servers (e.g. Paper) OR the proxy (e.g. Velocity), not on both.
• I have included a ViaVersion dump.
• If applicable, I have included a paste (not a screenshot) of the error.
• I have tried a build from https://ci.viaversion.com/ and the issue still persists.

[Barvalg]

Please update all Via* plugins from https://ci.viaversion.com/ .In case the issue still persists send the new dump and the issue will be reopened

[kodalee]

https://dump.viaversion.com/a76e2d20d088c5f278cfac34d3a628d20715dbc8b83f017a480a026ff4321b70

[Barvalg]

[kennytv]

This is needed as a direct replacement to the new movement packet

[kodalee]

The main problem there is that the explosion is very loud. Is there another substitute for this?

[kennytv]

Instead of putting it at 0 I can try putting it at the highest possible coordinates

[kodalee]

That would probably work. If its past the build limit then I see no possible way a player could see or hear it.

[kodalee]

More specifically if the Y-axis of the packet was put to the max then I would think that would be enough of a solvent. I would've done a change and PR but I have no idea how to modify packet translators haha