Hello!
When I started my modded FML-server (version: 1.7.10-10.13.3.1388, with around 45 mods, everything worked before) this morning I were so clumsy so I started with the minecraft_server.jar file instead of the FML-server.jar file. So it f***ed the world folder up. I had of course a backup or something and I mixed the files and when I started it again (in FML-server.jar) it starts with mixed blocks: