Sometimes your only option is to reset the world, removing the ghost blocks entirely and allowing the world to generate anew without them. This option is not always a sure fire fix to the issue. By doing this, it acts as a safeguard against possible corruption. What is basically does is bypass the halt by forcing you to acknowledge the issue before loading your world. Most of the times you can bypass this halt on your servers start by doing the /fml confirm command in console. If these block remain in your world, your server may have difficulties starting up. These items are referred to as ghost entities since entities remain even after a mod is remove. As the statement would imply, running a world with modded items installed on it but no longer with the same mods installed on the server will evidently break the server as it tries to load a world up with items it can’t recognize. If you don’t then you will encounter an error in the console similar to “this world has been saved with this mod but is not longer installed. When switching between different versions of the modpack or switching packs, you must also reset the world. Server owners typically encounter this error when running modpacks on their server and switch between various packs.

Show More Minecraft Error: Missing Mods In World

Missing minecraft 1.12 forge mods