Out of a total of 18 result rows in view Results (simple search content pane), 11 rows did not have their field_latlon set and therefore could not be shown on the map. The first row that could not be located was row #7 (nid #16575: ΑΓΑΛΙΑΝΟΥ ΜΑΡΙΑ). You can improve execution efficiency by using the Views UI to add an "is not empty" filter for field_latlon.