Links in title and descriptions made by SPARQL queries are most often red with the text "page does not exist" in the tooltip, even though the page does exist. It can be seen in the example in Help:Extension:Kartographer#GeoShapes via Wikidata Query and in my sandbox at dawiki at https://da.wikipedia.org/w/index.php?title=Bruger:Dipsacus_fullonum/sandkasse&oldid=9650381
Topic on Help talk:Extension:Kartographer
How strange. I created a task to have the engineers take a look. Thank you for the report.
Oh, I also created a task at almost the same time as you: https://phabricator.wikimedia.org/T202993