Server and Client not connecting

[Magor362]

Steps to reproduce

• Installed a Neoforge Server with the neoforge installer

• downloaded my modpack, modified it for Server use (no client side mods, and a few server side ones).
  https://modrinth.com/modpack/weich-server-modpack (unlisted and not intended for public use)

• added custom cobblegen config, which does work (atleast in Fabric 1.21.1, both client and server)

• did start the server and (after other issues with unremoved client mods) started without major visible issues

• tried connecting with the client side of the modpack over localhost, but got the mentioned Issue

error log about the connection

modlist.txt

Client side onscreen error message

Expected behavior

connecting of the client to the server without an error

Actual behavior

Error with message on Client:
Internal Exception: java.lang.UnsupportedOperationException: Payload cobblegen:ping_server may not be sent to the client!

Crash logs

latest.log

Mod version

[NEOFORGE MC1.21+] v5.3.10-BETA

Game version

1.21.1

Modloader

NeoForge

Other details

There is no problem connecting with cobblegen unlisted as a mod on the Server side

Acknowledgements

• I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open issue.
• I have written a short but informative title.
• I have updated the mod to version 5.3.10.
• I have admitted that I am a clown by having checked this box, as I have not read these acknowledgements.
• I have filled out all of the requested information in this form.