In order to better understand this issue, it would be great if you could check which URLs are getting loaded.
You can do this in your browser's Network console.
- Firefox: Menu > Web Developer > Network
- Chrome: Menu > More Tools > Developer Tools
After you're in, refresh your page in the WordPress Media Gallery and you should see the following:
Then, if any of those images were not found, you would see another value of status instead of 200 (for example 404). If so click on it and please check if the URL looks correct.
If it does not look correct (e.g. it is getting loaded from a different domain), you may need to update the WordPress domain: https://docs.bitnami.com/aws/apps/wordpress/administration/configure-domain/