That Atom feed does contain newer articles, but for some reason they don’t show up in NewsBlur.
The Icon Bar also has RSS feeds, so I tried adding those. When I try to do this however NewsBlur says:
This address does not point to an RSS feed or a website with an RSS feed.
Only the Atom feed can be added, but even if I delete it and re-add it, there are no new articles beyond 14th October.
If I go into “Site Settings” and click “PARSE THIS RSS/XML FEED”, it shows a 200 response, e.g.
2020-02-16 10:10:12 OK (200)
…yet no new articles appear.