The issue is caused when the page/post is saved with the original image and saved it publically then changed the image and now the original image needs to be replaced from what it pulled and to fix it the original URL of this post should be rest so the correct image can be pulled with the FB post.
Please also make sure to debug the URL for Facebook posts using this link: https://developers.facebook.com/tools/debug/
That would help you figure out the issues with your FB posts and learn how to fix it.