The national park is https://www.openstreetmap.org/relation/287917 .  It wasn't appearing on maps because an extra spur https://www.openstreetmap.org/way/42489097 had been added to the Lake District relation https://www.openstreetmap.org/relation/287917#map=17/54.24662/-3.28431 by mistake, possibly in https://www.openstreetmap.org/relation/287917#map=17/54.24662/-3.28431 .  I've fixed that in https://www.openstreetmap.org/changeset/96468358 and with a bit of luck it'll start appearing again soon.