I've added an untagged way https://www.openstreetmap.org/way/1429277102 and added it back to each of the relations.  This possibly wasn't the most efficient way of doing it, but it did work.
Unfortunately, the iD editor is not good at spotting gaps.  You can use overpass to detect problems - see https://community.openstreetmap.org/t/finding-broken-relations-with-overpass/129031 - and you can also use Josm's validator to do the same thing: https://www.openstreetmap.org/user/SomeoneElse/diary/406398 .