I just checked the link you provided and find the cause of this issue.
In this tweet, it has two links:
http://t.co/EW9jM0YeHW and http://t.co/Jbf5oQFDmX
And when importing this tweet, plugin will check the page of the first link to get the first valid image in this page. But the first link refers to the facebook app page that displays app content inside an iframe. So the plugin can not get any image here.
At present, JA Social plugin only checks image in the first link of tweet (as well as post in another sources), and do not attempt to get image from another link if the first link returns no image since it can be a cause of very slow processing.
For temporary solution, you might need manually update image for these items. I’ll report to dev team this case if they can find a solution for it in the upcoming version.