Joining a 1.21.5 server kicks me out with a "Network Protocol Error"

[Zpiboo]

General Information

ViaVersion dump: https://dump.viaversion.com/d02c872d72c6d7e44171406bf80db653656b26d7001001fa5e43b9d8cfb9f024
debug/disconnect-... crash report: https://mclo.gs/mbSdxxf

Bug Description

I usually play on the parkour mode of this server called Rinaorc.
They haven't updated the Parkour server in a while: it supports every version starting from 1.8.9 up to 1.21.5.
The main lobby supports all versions up to 1.21.11, though.

When I select version 1.21.5 in VFP, I'm able to join the server just fine. From the lobby, if I try to join the parkour server, I get kicked with a "Network Protocol Error".
It didn't cause any problems in the latest fabric 1.21.11 VFP version.

Steps to Reproduce

1. Select VFP version 1.21.5
2. Join play.rinaorc.com
3. Right click on the first item in the hotbar, and click on the ladder in the menu that appears
4. You're kicked out of the server

Expected Behavior

There should be no "Network Protocol Error".

[Barvalg]

[nanobatch]

Having the same issue here, but I'm trying to connect to a 1.21.11 server from 26.1. I can't join the server at all in this version though.