The official correct boundary is https://www.openstreetmap.org/way/254310728

Looks like the other boundary, which is currently visible in a straight line, was fixed in https://www.openstreetmap.org/changeset/96719145, specifically with the change to Newfoundland and Labrador relation (391196). I'm not entirely sure how that would have fixed it, but larger OSM relations can be a bit of a dark art. That change was done about a day ago, so the rendering should be hopefully fixed within a couple of days.