Thumbnails not displaying

I’m running WordPress 4.9 and WP Latest Posts version 4.2.1 (free). I’ve had two recent posts on my site where WP Latest Posts failed to display the corresponding thumbnail images. (You can see what’s happening by following the link I’ve included with this post.)

WP Latest Posts is taking thumbnails from the first images in these post. The site isn’t using Featured Images.

Nothing different has been done in creating these posts vs. all of the previous posts on the site. Can you advise on how to get the thumbnails to display properly?

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