Have you ever done a post and maybe forgot to add your featured image? Then, when you or someone else shares it on Facebook, it pulls in the wrong one?
Or maybe you changed that image after publishing and you cannot get new shares on Facebook to reflect that change.
Of course, there are some plugins that will let you choose the image specifically that will appear there, for example Yoast SEO. But still, there are times when the bugger is just too damn stubborn.
Here’s my tip. In the case of it pulling in the old one, make sure you have deleted it from your media gallery. Then, go to the Object Debugger, Facebook for Developers (don’t worry if you are not a developer) and put the URL in there and see if the new one comes up in the report. If not, scrape it again by pushing the button. Chances are good, this will solve your problem.