Problems spawning monsters into a location

Hello, people!

So, I have made the monster entry in monsters, I’ve put the monstergroup up. When I place the monster via console command it gives me the correct monster and the correct loot, I just cannot made it spawn in the map. I put this in the .json for the map square:

"place_monsters": [ { "monster": "GROUP_SERVITORS", "x": 4, "y": 14 } ],

The monstergroup is this:

        "type" : "monstergroup",
        "name" : "GROUP_SERVITORS",
        "default" : "mon_servitor",
        "monsters" : 
    { "monster" : "mon_servitor", "freq" : 10, "cost_multiplier": 1}

The square is part of an overmap special. Why the monster won’t spawn? There are no error messages, the mon_servitor just won’t spawn!