I added a new subpage link as I would normally have added a regular link. And what got there is broken wikitext which doesn't render as a link. Not sure yet if this is a VE issues, Parsoid issue, or something broken in both.
What was the page to which you linked? Did you try to use wikitext inside the visual editor (linking to "./Attributes of a good ED"), or did you use an actual (albeit red) link suggestion of "Revolution of 2016/Attributes of a good ED"?