As I understood it Facebook would like to make an extra buck if you’ll be posting YouTube-links, thus not exposing your post to as many as if it were a Facebook post, wanting you to pay for an ad to extend the exposures.
One “fix” to this should be to just put the thumbnail and the description/caption in you post and then put the actual YouTube link in the first comment to that post.
One “fix” to this should be to just put the thumbnail and the description/caption in you post and then put the actual YouTube link in the first comment to that post.