[Users] Some URLs will not open in viewer

[Claws mail user]

Apologies if this is a re-post my original message did not seem to
appear 

In Claws mail v. 3.13.0 some URLs in HTML emails will open a Web page
in the viewer when you click on them and some won't. This is using the
Fancy plugin with the option "Open in viewer (remote content is
enabled)" selected. Everything else is enabled: display images, execute
java script,execute java applets, render objects using plugins. I'm not
sure I can see any common thread amongst the links that will work
with the viewer and those that won't. If you right click on a link
which won't display in the viewer and choose "Open in browser" this
pretty much always seems to work. A right click and "Open in viewer"
sometimes works if a direct click on the link doesn't work. Is there a
reason for this or a configuration option which will fix it? Many
thanks