On our website, we switched to a new CDN to host our images and ever since then images does not show up in sharer. There are 2 different behaviors we are experiencing:
- Image does not show up in sharer until second attempt.
- Some images never appear, doesn't matter how many attempts. the only thing that makes them appear is manually "clear" the Facebook cache by using the Debugger.
For the first problem: I understand that Facebook doesn't wait until processing the image is complete before it cancels the attempt to place the image thumbnail into the sharer and this is by design and is done to speed up the post creation process.
For the second problem: This is a bit strange, it seems that the sharer never succeeds caching and processing the image therefor never displaying it. But it does show it after using the Debugger.