That’s the image URL to which you were referring in the OP.
The flow for this process is:
- User posts the topic URL to Facebook
- Facebook retrieves the topic URL and parses the opengraph tags
- Facebook identifies the og:image URL
- Facebook attempts to retrieve the og:image URL
- Facebook resolves the URL’s hostname into an IP address
- Facebook connects to the IP
- Facebook retrieves the URL
If it’s trying to retrieve the URL https://d11a6trkgmumsb.cloudfront.net/optimized/4X/e/0/4/e04203d665f3ff3540361fdeedb76df8cf37df9b_2_1024x767.jpeg but gives the error Could not resolve the hostname into a valid IP address. Discourse is not in the path for that step of the process. It’s Facebook’s servers trying to resolve an Amazon Cloudfront hostname.