When sharing a post to Twitter, you may occasionally find that the image is not shared with the post.
In order to better serve its customers, Twitter will parse URLs shared to its service and verify that the content is what it is claimed. This includes sourcing an image from the shared link and using that as part of a "Twitter Card" when presenting a link. If the image is missing, it is usually the result of Twitter being unable to find the metadata tags it needs for a full card.
When set to "Allow Twitter to Extract the Metadata", Twitter scrapes the associated permalinks behind each of these posts for metadata tags which it can use to construct a Twitter card. You can test this by pasting the permalink into Twitter's Card Validator. For both posts, Twitter is unable to extract an image to populate the card with, which is why you're not seeing the image when sharing the post.
To workaround this, you could set the post to "Submit an Image Along With a Tweet" for each of these posts. This way, Twitter is given the image from your community as well as a shortened link to the external permalink and any share text entered by the user. The default setting for new posts in the community can be set to "Submit an Image Along With a Tweet", just ask your CSM or the Dynamic Signal Support Team for assistance.