I believe I know what this problem is. I had the same problem with the Pinterest button not connecting the image. If a “featured image” is not set on your post, Social Media Feather will not connect with any image from the post and the pin will not have an image.
Most plugins have a back up setting that will list all of the images on the page that you can choose from if the feature image is not set.
Hope this helps!
I would like to know how you are using W3TC/Cloudfront/Cloudflare in a little more detail.
Could you share with me your set up? Are using managed hosting plus CloudFront? Is it set up so CloudFlare looks for the content first and then it goes to CloudFront? What type of hosting are you using?
Any help would be wonderful!
Thanks!