"By default, when you change the properties of the node associated to a body, there will be no effect. " - - - from the Performance Tips | Babylon.js Documentation
// By default, the body.disablePreStep === true
body.transformNode.position.set(0, 10, 0);// no effect
// But -->
console.log( body.transformNode.position ); // {_isDirty: true, _x: 0, _y: 10, _z: 0}
// So how can I get the correct position of one body