Hi @mastafu
I think that’s because you’ve set the function, but never execute it. Could you please try it like this:
// add markers
$markers.each(function(){
add_marker( $(this), map );
});
// center map
center_map( map );
// add marker cluster
markerCluster( map.markers, map )
// return
return map;
Because this issue is more related to Google Map, kindly get in touch with Google Maps community for further support.
Thanks 🙂