When I select a website that shows extensions that need to be updated the popup dialog is blank and the update does not happen. When I select any task to perform again nothing happens and the popup screen is also blank.
Please, check if you have this setting in htaccess protection: HTTP Headers Protection -> X-frame options -> DENY. If so no popups are allowed to be shown. In this case change it to SAMEORIGIN or NO, save the changes, delete the .htaccess file and apply protection.
But Control Center is not installed on all webs, and this setting prevents iframes, so this is causing the issue. Set it to SAMEORIGIN and only iframes coming from your website will be allowed. This will keep security high.