Facebook error when pulling og:image
For other people who end up here, I encountered this issue temporarily. The Facebook Sharing Debugger fetches images asynchronously and can give false 404s.
I recommend scraping again a couple of times to confirm.
After some time I was able to solve the problem. It turns out, the FB Sharer doesn't accept base64 images. What I was doing was directly saving the base64 binary to S3, and because of that FB couldn't display the image.
So if someone out there is doing the same thing as I was, save your base64 images to file/directory first before uploading it to S3.