I have the same issue when I publicize a post to Facebook ... it's like Russian Roulette ... sometimes it uses the Featured Image I have designated ... sometimes it does not ... when I run the URL for the posts in question on the FB Debugger ... it shows the correct Featured Image ... with no errors ...
Conversely, if I manually share the post to my FB page, or if I use the jetpack FB share link in the post itself ... it always uses the proper image.