on one of the domains lets say : 46.165.192.132 we are using ngnix for production sites. We have installed virtualmin on another IP 46.165.192.180 for dev and test sites. However, the virtualmin tends to assign the first IP ending with 132 as a default ip which cause the server to get down and apache is stopped.
Yeah, by default, Virtualmin assumes that Apache is the only running web server on your system, and it also assumes that your domains would go in the first IP address found on your system.
You can tweak those defaults though – to do that, go into System Settings -> Virtualmin Config -> Network Settings. In your case, it sounds like you may want to change “Network interface for virtual addresses”.