1.8.9 client cannot join 1.12.2 server

[BestMark]

/viaversion dump Output

https://dump.viaversion.com/39f07558167e9d0c160b2943579ea52be0baf052d4a304de1f77bebab266664a

Console Error

https://mclo.gs/jjjHGJd

Bug Description

1.8.9 client cannot join 1.12.2 server

Steps to Reproduce

1. Login with 1.8.9 client
2. Join 1.12.2 server with latest ViaVersion, ViaBackwards and ViaRewind from Jenkins.

Expected Behavior

You cannot join the server

Additional Server Info

No response

Checklist

• [X] Via plugins are only running on EITHER the backend servers (e.g. Paper) OR the proxy (e.g. BungeeCord), not on both.
• [X] I have included a ViaVersion dump.
• [X] If applicable, I have included a paste (not a screenshot) of the error.
• [X] I have tried the latest build(s) from https://ci.viaversion.com/ and the issue still persists.
• [X] I have looked at https://www.spigotmc.org/resources/viarewind-legacy-support.52924/ and it does not offer a fix for my problem

[Barvalg]

[FlorianMichael]

Can't reproduce, seems to be a plugin issue.