Wordpress not showing thumbnails

I am using the Plugin Auto Featured Image to set thumbnails automatically. And in the database it shows updated meta thumbnail key.

But for some reason it is not showing the featured image. It doesn't show a "placeholder" neither. It just shows nothing at all.

Also, when I try to view the attachment on a single page, it does not show it.

How can I proceed to find the problem? If you need more screenshots of different tables on my database, please ask. I really appreciate your time.