Hello,
Something is strange, unlike the others lakes, the Lago Maggiore is not rendered in the usual blue on maps.wikimedia.org, see : maps.wikimedia.org https://maps.wikimedia.org/#11/45.9067/8.6071
(I've looked directly at the tags on OpenStreetMap and the same tag present on other lakes seems to be present too : https://www.openstreetmap.org/relation/11758#map=10/45.9516/8.6737 , so I don't see where the difference of rendering comes from).