Hi,
Please find this code sf-post-formats.php at /dante/includes/
$post_item .= '<div class="blog-item-details vcard author">'. sprintf(__('By <span itemprop="author" class="fn">%1$s</span>', 'swiftframework'), $post_author) .'</div>';
Change to:-
$post_item .= '<div class="blog-item-details vcard author">'. sprintf(__('By <span itemprop="author" class="fn">%1\$s</span>', 'swiftframework'), $post_author) .'</div>';
Thanks
Mohammad