See: Modflower/polysit#7 as initially reported by @ArkoSammy12

Steps to Reproduce:

• On server:
  • Use Minecraft 1.20.4
  • Install Fabric API, ViaFabric, ViaRewind, Polymer, any Polymer-based mod (i.e. Polysit, Polyfactory)
    • It seems that any registry modification is required, as bare Polymer doesn't trip the bug.
• On client:
  • Use Minecraft 1.20.2
  • Install Fabric API; the vanilla client seems unaffected
• Start the server with the given mod set
• Join the server

Expected results:

As a vanilla client would do; join perfectly fine

Actual results:

Claims a conflict on the Minecraft namespace regarding the Breeze and Wind Charge.

Other things of note:

The registries it conflicts on seems to always be the registry modified by mods

• Polysit only trips the entity registry
• Polyfactory trips the block registry

It seems that 1.20.1 clients get mangled entity data handlers

Logs:

From server - not particularly helpful for more than versions

From client

ViaVersion dump

marked the external issue as "help wanted" cuz the via dev team refused to do anything with it, as for myself - i do encourage requesting for help on how to solve it.

I imagine it doesn't fully cancel full logic, but to be fair it also is kinda issue on ViaVersion part for not canceling that packet entirely

Fair; was just about to duplicate this issue there in case it was more their end rather than yours.

Fixed.