Right now my working solution for the problems is the following,
After creating a virtual server every time I have to go to /etc/apache2/sites-available and edit the “*.conf” file related to the particular virtual server.
and change <VirtualHost 128.xxx.xxx.227:80> to, <VirtualHost *:80>
It would be great if you can let me know a permanent fix to this problem by changing some settings or something.
As long as all of your sites use either IPs or *:80 (and *:443) and you choose the matching option in Virtualmin config, this will never happen again, even on Virtualmin upgrades as documented in the comment you linked.