[1.20.4->1.20.1 and below] Player block collision does not work on some servers

'/viaversion dump' Output

https://dump.viaversion.com/69ffb945142cd2ac65115b5d7defaa8d8c8a3ed7b55b91bb5bd843fcabba1cdd

Console Error

No useful errors or warnings can be found in ViaProxy logs.

Bug Description

Translating 1.20.4 down to 1.20.1 and below will cause block collision to stop working on some servers for unclear reasons.

No errors or warnings are printed to ViaProxy's logs.

This is happening on the "Hololive Construction" server (mc.holocons.xyz), currently running Paper 1.20.4 and Velocity.

Specifically, everything works fine in the hub server, but block collision somehow breaks in both the Creative and Survival servers. More information including precise versions and plugin list is attached below.

Steps to Reproduce

Open ViaProxy.
Connect to mc.holocons.xyz using a 1.20.1 or lower client, picking the "1.20.4" option in ViaProxy as that is what the server is currently running.
You will be connected to the hub server, where everything works as expected.
Join the Creative (recommended because you can fly) or Survival (you'll be stuck in place) servers from the hub server.
Block collision is completely broken, including both the floor as well as walls (you can test this using Creative mode flying)

I got these test results using:

ViaProxy 3.3.2 dev CI build 429
Minecraft 1.20.1 vanilla client
Java 21
Windows 10

I have confirmed that this happens with a completely bone stock ViaProxy setup with default config and no plugins (the dump has a modified config, but the result is the same).

Expected Behavior

Block collision should work.

Additional Server Info

I am using ViaProxy, latest dev CI build 429.

The server at mc.holocons.xyz is running:

Checking version, please wait...
This server is running Paper version git-Paper-496 (MC: 1.20.4) (Implementing API version 1.20.4-R0.1-SNAPSHOT) (Git: 7ac24a1 on ver/1.20.4)\nYou are 1 version(s) behind\nDownload the new version at: https://papermc.io/downloads/paper\nPrevious version: git-Paper-462 (MC: 1.20.4)
Velocity 3.3.0-SNAPSHOT (git-9d25d309-b400)
Copyright 2018-2021 Velocity Contributors. Velocity is licensed under the terms of the GNU General Public License v3.
velocitypowered.com - GitHub

Here's the plugins list of the servers, obtained using the /plugins command.

Hub (block collision works fine)

Server Plugins (14):
Paper Plugins:
 - SignedVelocity
Bukkit Plugins:
 - CMI, CMILib, CustomJoinLeaveMessages, floodgate, LuckPerms, PlaceholderAPI, Plan, PlayerParticles, ProtocolLib, Vault
 voicechat, WorldEdit, WorldGuard

Creative (broken)

Server Plugins (22):
Paper Plugins:
 - SignedVelocity
Bukkit Plugins:
 - BookExploitFix, CMI, CMILib, CoreProtect, CustomJoinLeaveMessages, FastAsyncWorldEdit, floodgate, HoloItems, HsRails, ItemSwapperPlugin
 litematicaprotocol, LuckPerms, PlaceholderAPI, Plan, PlayerParticles, PlotSquared, ProtocolLib, spark, Vault, voicechat
 WorldEditSelectionVisualizer

Survival (broken)

Server Plugins (44):
Paper Plugins:
 - SignedVelocity
Bukkit Plugins:
 - CarnivalHelper, Chunky, Citizens, CMI, CMILib, CoreProtect, CustomJoinLeaveMessages, Denizen, EntityDetection, floodgate
 Graves, GriefDefender, HeadTextureFixer, HoloItems, HsRails, InventoryRollbackPlus, LibsDisguises, litematicaprotocol, LuckPerms, LWC
 MMOItems, Multiverse-Core, Multiverse-NetherPortals, MythicLib, MythicMobs, packetevents, PlaceholderAPI, Plan, PlayerParticles, ProtocolLib
 pvparena, PvPToggle, ResourceGuard, spark, SpecializedCrates, StackMob, Vault, VillagerLobotomizatorNator, voicechat, VoidGen
 waypoints, WorldEdit, WorldGuard

Checklist

[X] Via plugins are only running on EITHER the backend servers (e.g. Paper) OR the proxy (e.g. Velocity), 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 a build from https://ci.viaversion.com/ and the issue still persists.

ViaVersion / ViaBackwards