The problem is caused by incorrect HTTP and HTTPS configuration: https://domain.com is the actual site URL, however, http://domain.com is used in Dashboard > Settings > General. In this case, it is necessary to configure URLs correctly.
If your site is HTTPS and you have images with HTTP, you need to delete these images and upload again so that they could get HTTS.
If you have any questions please feel free to contact us.
Most likely, you uploaded the demo, when your site was on HTTP without SSL certificate, then you configured SSL certificate and got HTTPS as the result, images had HTTP and they should be reloaded.
If you have any questions please feel free to contact us.