Not all comments show in ‘Recent Comments’ sidebar widget

Hi,
I have just noticed that comments on media pages dont show in the ‘recent comments’ sidebar widget (although they do show in the RSS feed). For example, on the above page, about half way down is an image ‘Prussian campaign medal’. Click it to go to the media page. There are two recent comments but neither shows in the content sidebar widget.
https://battlefieldanomalies.com/the-battle-of-koniggratz-2/12prussian_medal/

The page I need help with: [log in to see the link]