The server doesn't need to synchronize anything. Synchronizing (enet_ent_synchronize()) does nothing more than creating all the global entities that exist on the server on the clients. You should test if enet_ent_create() is called after the client connected or if the entity only gets visible then (you can use the debug panel, ent row, to look if an entity was created and the error() function or the debugger to check if enet_ent_create() was called).