Not all posts get a featured image?

Hi!
First, thanks for a great plugin! This really helped adding the featured images to my blogposts, after importing them from blogger and importing the images used in the posts as well.
There’s only one problem, some of the posts aren’t getting updated. Although they have an image within the blogpost, the plugin won’t set a featured image.
Have you got any idea what’s happening here?

Thanks for your help!

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