First of all thanks for nomination! For dots of Milan, Minsk, Athens and Copenhagen, I am trying to detect problem and find a solution with help of some seniors.
Check the Id of the dots, they need to match the hint of your answers. You can also set the class=zoomable-circle and make them bigger, which will retain the size of dot when the map is zoomed.
Porto, Valencia, Sevilla, Malaga (only in Iberian Peninsula)