Spawngroup modifications (Linked to MES) are no longer taken into account by MES once the world has been created, we have to recreate a new world for the new modifications to be taken into account...

Example :

Create a world with a spawngroup
Then start the world
Edit your spawngroup mod add new...
Restart your save world

Problem: the new spawngroup you added will not be there (To get it you will have to recreate a world)