I am having a very similar problem in Version 5.12.88. I have three specific posts selected to display at the end of this post, link here:
After removing the first “related post” from my site completely (trashed, then permanently deleted), I have a stuck picture with a re-direct link back to the same post. I’ve gone back into this post and reselected 3 new specific “related posts” to display, but this first image spot seems to be holding on to the deleted post.
Any help would be appreciated.