Running ViaBackwards on a 1.21.11 server causes players to become invisible

[Zumbuh]

'/viaversion dump' Output

https://dump.viaversion.com/9456c3b93305c2334cb1da44117a33db1a1370ac16b01a667ebe356abdb2a8a3

Server/Client Error

https://mclo.gs/9mxrZoV

Bug Description

Players will become invisible when the server is on 1.21.11 and ViaBackwards is installed. There are no errors within the server console when this happens, but there is a client error about adding a player before sending the player info. This does not occur when ViaBackwards is not installed. I've tested this with 1.21.8 clients and 1.21.11 clients.

Steps to Reproduce

1. Put ViaVersion and ViaBackwards on a 1.21.11 server.
2. Login two or more players.
3. Teleport away from the player, then teleport back.
4. The player will be invisible.

Additional Server Info

I do use Velocity, but Via plugins are on the Purpur server, not Velocity. I have also tested with zero Velocity plugins and the issue persists.

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]

Athena Log Analysis

Platform Information:

Property	Details
Contains Via	❌
Platform Type	unknown
Is Proxy	❌

[Kichura]

Can't reproduce on my testing server:

This will be down to one of your clients being modded or one of your server configurations are wrongly set up somehow.

[Zumbuh]

I am on a regular Purpur server with no mods on my client.

[Kichura]

I am on a regular Purpur server with no mods on my client.

Can't reproduce on purpur either.

[Zumbuh]

I have deleted:

bukkit.yml
spigot.yml
config folder
purpur.yml

One at a time to allow them to regenerate, and the problem was still there.

I have also created a new server from scratch with the Purpur jar and only Via plugins (still under Velocity, using default configs) and the problem is still there. After entering a Nether portal and returning, the other player(s) are invisible.

viabackwards.mp4

[Kichura]

I have deleted:

bukkit.yml spigot.yml config folder purpur.yml

One at a time to allow them to regenerate, and the problem was still there.

I have also created a new server from scratch with the Purpur jar and only Via plugins (still under Velocity, using default configs) and the problem is still there. After entering a Nether portal and returning, the other player(s) are invisible.
viabackwards.mp4

There's a problem with this video:

1. That video was created with same version as server meaning ViaVersion at this point would've disabled itself.
2. I tried to do the exact same thing as your video and nothing is different.

mc.mp4

Meaning your issue seems insufficient from what i can tell, Did you modify velocity proxy in any way? (force-key-authentication is false, forwarding mode is modern and ofc lobby is the only server available on my end)