@ scott
This sounds like they’ve uploaded images that are too large and when Connections tries to create it’s thumbnail WP (PHP) runs out of memory and stops. If that is the case…
The solution is to log into your site with FTP and navigate to the following folder:
../wp-content/uploads/connections-images/
Find the folder for that entry and open it. Download the originally uploaded image and download it. After you download it, reduce its size and reupload it overwriting the original.
Now the entry should show.
Just yesterday I added two new features in version 8.1.6 to help address this.
The first, it will no longer allow a user to select an image larger than the server supports being uploaded.
The second, images right after being uploaded will be checked for their size. If they are above 1920x1080px they will be scaled down.
I believe both of these will help reduce the issues like this even further.
Hope this helps, let me know.