My URL passes the Card Validator (example URL: http://learn.code.org/sh/15259267), but shows a broken image in the Card Preview.
I’ve validated that the twitter:image content is a valid URL (http://learn.code.org/assets/flappy_sharing_drawing-897bbc87371c71c24f755ecc832e645b.png).
This works elsewhere on our site, the difference being that elsewhere we use dynamically generated images whereas this is a static images. An example of a working link is http://learn.code.org/sh/158581.
I believe that the static image version had been working as recently as a couple weeks ago, but I’m not 100% certain of this.
Please advise as to what could be causing this problem.