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If you are seeing some images and not others, your server is telling your browser to no longer display the unsecured images.
You can verify by right clicking on the image or placeholder that does not display and the select your browsers Inspect option in the dropdown. Do you see a url that begins with http:// (unsecured) in the inspect code?
Now try this for an image you can see. Do you see https:// (secured) instead of http:// ?
If yes to both of your above tests, any changes made to httpd.conf or .htaccess to enforce TLS result in the browsers no longer being allowed to display unsecured content. That is because it will only honor secured content.
There is another possibility for this symptom.
If you renamed all http:// in your database dump to https:// as recommended above, but the external server associated with one of the url that you changed does not support https://, the associated content may not be served to your browser. It may even produce an error.