AGigante

I have had the same problem…
Deactivate the Photon Jetpack plugin would fix the issue.
(click on “learn more” and the “deactivate” button will appear)

I forgot to comment that I have added as well content-smallthumb.php and content-bigthumb.php the following:
echo 'Posted by <a href="'. get_author_posts_url(get_the_author_ID()) .'" title="'. sprintf(__("Posts by %s","gamepress"), esc_attr(get_the_author())).' ">'. get_the_author() .'</a> | ';

Thanks again