A post whose source is a direct link to a Facebook image, rather than to the Facebook post containing the image. These are considered bad links because there's often no way to find the original Facebook post from the image link, and the hashes of URLs will expire after a period of time.
If you see this warning while uploading, make sure to change the direct image link in the source field to the Facebook post where you found the image.
Some image URLs correctly resolve to a post ID, but many don't while not being a Bad Facebook ID; make sure to check the direct image link on sources to see if it's a bad ID or just a bad link.
