I turned this new option on, and it works very well on the homepage, and it displays default thumbnail image when there is no feature image. But when I enter in a post, the extract below of "most popular posts" or "similar posts", don't show the default thumbnail image, and the space for image is empty. Is it a bug ?? thanks for your answer !
Thanks for the reply. Would you be so kind to put this in the striking 5.1.8 error report section? I think you found a omission we did not check before releasing the theme update.