Connectivity Problem with Minecraft - Unable to connect to the server after switching to neoforge

System Information

Field Value
Operating System Linux - Debian GNU/Linux 13 on x86_64
Product AMP ‘Proteus’ v2.8.0.2 (Mainline)
Virtualization Docker
Application Minecraft
Module MinecraftModule
Running in Container Yes
Current State Ready

Problem Description

Issue

The server was running vanilla version 26.2; I switched it to 26.1 and then to NeoForge while adding mods, but now I can no longer connect.

Reproduction Steps

  • Downgrade the server from 26.2 to 26.1
  • Switching from vanilla Java to NeoForge 26.1.2.78
  • Add mods by creating a “mods” folder and placing them inside it.