Comment on SEO Recent Posts WordPress Widget by Andrei.

WordPress Popular Posts Widget Options Thank you.
But now I have some issue. Please check
There are 2 first posts which I inserted a thumbnail and featured image. After that I made a regenerating. But they are didn’t display. Please help to solve it.

Also I don’t quite understand why should I use a featured and/or thumbnail img. Thumbnail is not generated automatically if I only use a featured img?