I had this issue previously and it was fixed, but it seems to have come back with the latest Virtualmin update.
I made a back up and tried to restore on a different server with different IP.
the /etc/nginx/sites-available/domainname.com file doesn’t seem to update the following lines:
listen xx.xx.xx.xx.;
The fastcgi_pass unix:/var/php-nginx/xxxxxxxxx.sock/socket;