I'm moving my issue to this thread as I have confirmed it still happens with the release installer, not just the beta vm6-install.sh installer.
On Debian 9 LEMP install (invoked with 'bash install.sh -b LEMP'), apache2 is pulled into the install preventing nginx from binding to port 80 and the install fails.
My basic install path is as follows:
My VPS host does not have a Debian 9 image, so I install a Debian 8 Minimal image. I perform some post image install steps such as creating new users, setting up passwordless ssh logins and the like. I then update all Debian 8 packages, and then change /etc/apt/sources.list to use Stretch, and dist-upgrade to Debian 9.
Prior to installing Virtualmin, my /etc/apt/sources.list contains the following:
deb http://ftp.debian.org/debian stretch main contrib non-free
deb http://ftp.debian.org/debian stretch-updates main contrib non-free
deb http://security.debian.org stretch/updates main contrib non-free
A listing of installed packages prior to running the installer can be found at https://pastebin.com/RqChqCS0 .
Here is the full virtualmin-install.log up to the point of failure. https://pastebin.com/9w7QckqA
I guess something the installer wants is pulling in apache2 as a dependency.
Let me know if I can help with any testing.