I have also just noticed that the browser Title (Chrome) is showing a different domain name than the one I’m logged in as (also a domain on this box)
Yet under Virtualmin it is showing the correct domain and the correct domain summary location.
It is as if it is logged in as a different domain (but I’m logged in as root (not the client owner of the domain)
If you go to example.com - Server Configuration ⇾ SSL Certificate page do you see the button to Copy SSL certificate to Services … ? If you do, click it. It will copy SSL certificate from the virtual server to be used with Webmin and other services.
When done, close current Webmin tab and re-open it. Do you have it working now?