The QGIS atlas defined with PyQGIS and a QPT template exports the same maps

I need to generate an atlas for each feature from a layer for reporting. There will be created a few maps. The centre of each map must be focused on each feature. In this task I use a predefined QPT template. In QGIS Composer Manager everything works perfectly. Then I save the QPT file as a template and I try to automate the process with a plugin using this function. It’s based on this thread: Programmatically load composer from template and generate atlas using pyQgis

    alayer=iface.activeLayer()
    # Add all layers in map canvas to render
    myMapRenderer = self.iface.mapCanvas().mapRenderer()

    # Load template from file
    myComposition = QgsComposition(myMapRenderer)
    template = 'atlas16.qpt'

    myFile = 'C://Users//maria//.qgis2//composer_templates//atlas16.qpt'
    myTemplateFile = file(myFile, 'rt')
    myTemplateContent = myTemplateFile.read()
    myTemplateFile.close()


    myDocument = QDomDocument()
    myDocument.setContent(myTemplateContent)
    myComposition.loadFromTemplate(myDocument)

    # Get map composition and define scale
    myAtlasMap = myComposition.getComposerMapById(0)


    # Setup Atlas
    myAtlas = QgsAtlasComposition(myComposition)
    myAtlas.setCoverageLayer(alayer)
    myAtlas.setComposerMap(myAtlasMap)
    myAtlas.setEnabled(True)
    myAtlas.setHideCoverage(False)



        # Generate atlas
    myAtlas.beginRender()
    for i in range(0, myAtlas.numFeatures()):
        myAtlas.prepareForFeature( i )
        jobs = "D://Krzysztof//Skrypty//Archiwum//"
        output_jpeg = jobs + str(i)+ "_BMS_plan.jpg"
        myImage = myComposition.printPageAsRaster(0)
        myImage.save(output_jpeg)
    myAtlas.endRender()

    if os.path.isfile(output_jpeg) is False:
        QMessageBox.warning(self.iface.mainWindow(), "Uh Oh!", "Something went wrong, no image exported!")
    self.dlg.close()

In the result I get some reports, but they look same – so the focusing on points isn’t performed.

I suspected that I might be caused by the extent which is present in the QPT file. Then I changed my function, so that the extent will be adjusted for each feature. However, at the end I got only empty reports.
The template content is as follows:

Does anyone know what might be wrong? Could you give any hints how a QPT template should be adjusted?

myAtlasMap.setAtlasScalingMode( QgsComposerMap.Auto )