mongoose update nested document not working

i try to figure out what I'am doing wrong that moongose is not updating my document. Just for testing the id's are hardcoded.

node.js

   var id1 = "592fd471fedd311d5c76a024";
var id2 = "592fd4ad608e001d79938ba8";

Workshop.update(
    { _id: id1, 'themen._id' : id2},
    { '$set':
        { 'themen.$.risikolandschaft': ["John", "Doe"], }
    },
    function(err,body) {
        if (err) { console.log(err) }
        else { console.log(body);}
    }
);

here my data copied from MongoDB Compass

_id:592fd471fedd311d5c76a024
    bezeichnung:Workshop 1.5.2017 / 10:46
    themen:Array
        0:Object
            thema:Object
            risikolandschaft:Array
            date:2017-06-01T08:47:41.944Z
            _id:592fd4ad608e001d79938ba8
    stammdaten:Array

the log from body

{ n: 0, nModified: 0, ok: 1 }

"mongoose": "^4.8.6"

via miholzi