Any page with certain external images takes ages to load (usually over 20 seconds!), e.g.
https://www.dokuwiki.org/popularity and
https://www.dokuwiki.org/template. This only happens when the images return either a "no-cache" or "max-age=0" or similar. See also a discussion about it here:
http://irc.dokuwiki.org/index.php?d=2012-11-24#msg427041