I just found the “download remote images threshold”, which is set to 10%, it is possible that, when the post causing the problems was posted, the the disk usage was above 90%,
/var/lib/docker was moved to a separate, large, partition last week, however using “Rebuild HTML” as an admin user hasn’t resulted in this being solved for this post when the first external link is to:
But I note that in this case the URL is a HTTP one that serves a Redirect to HTTPS:
lynx -head -dump http://www.progcode.org/
HTTP/1.1 301 Moved Permanently
Date: Mon, 17 Jul 2017 08:55:44 GMT
Expires: Mon, 17 Jul 2017 09:55:44 GMT
So is there an issue with Redirects, in the code that tries to download images, for use as thumbnails?