Featured image from RSS syndicated article

Hey guys.

I am having issues with my articles sourced from RSS. I have a site that is obtaining posts from an RSS feed. The feed contains media files [e.g. 2209724-16×9-940×529.jpg (JPEG Image)]. To source these articles, I am using FeedWordPress, which gets the files and then inserts them into my posts.

The problem now, is that I try to then, use the first image on the post, as a featured image. Either automatically or manually, it will not work.
Automatic attempt courtesy of code from wp-snippet.com:

function autoset_featured() {
          global $post;
          $already_has_thumb = has_post_thumbnail($post->ID);
              if (!$already_has_thumb)  {
              $attached_image = get_children( "post_parent=$post->ID&post_type=attachment&post_mime_type=image&numberposts=1" );
                          if ($attached_image) {
                                foreach ($attached_image as $attachment_id => $attachment) {
                                set_post_thumbnail($post->ID, $attachment_id);
                                }
                           }
                        }
      }
add_action('the_post', 'autoset_featured');
add_action('save_post', 'autoset_featured');
add_action('draft_to_publish', 'autoset_featured');
add_action('new_to_publish', 'autoset_featured');
add_action('pending_to_publish', 'autoset_featured');
add_action('future_to_publish', 'autoset_featured');

Manual attempt:
Open post
Set image
Select “set Featured image”
Select image from media library
^^ “this is an image in post from RSS. I have not manually uploaded”
Set featured image.
Media library closes – no result. It does not update.

What I’ve tried:
– Disabling theme and trying with another theme (same issue)
– Tried using an image that was manually uploaded – WORKS.

Is there any possible cause for this. Any help would be appreciated.