I had a friend run into that same issue before and I was able to fix it by doing a DB repair. Have you tried that yet?
If not add this to wp-config.php
define('WP_ALLOW_REPAIR', true);
Then make sure you’re logged in and visit yoursite.com/wp-admin/maint/repair.php
If that doesn’t work can you post what is shown in your htaccess files? Could be an issue there…
Here’s someone with the same question, but that was never answered.
Also, when you click on one of those images what does it look like?
What is the file type shown? And if you copy and paste the actual url of the image in the browser does it work? It could be registering the wrong file type. For example, I know that some CDN’s use webp images which is somewhat of a newer technology and I’m not positive that wp would recognize those.
The last option I can think of is making sure your database prefix hasn’t changed. In your old site if your wordpress config had this: $table_prefix = 'wp_'; and then you exported your content to your new site which had, say, $table_prefix = 'xyz'; this would cause the issue you’re having because for instance wp_posts would have been changed to xyzposts. You can fix this by exporting your old sql posts and bulk manually changing the prefix with grep / find in the terminal or some sort of editor like sublime.