I upgraded to webmin-virtual-server 6.07.gpl on Ubuntu 16.04 and now every hour my php/fpm setting break all the web sites.
I was using pipes, but it forces the config over to ports and increments the port numbers every hour. It does NOT change the apache port references, so each web site that uses PHP stops working.
My former setup looked like this:
$ grep sock /etc/php/7.0/fpm/pool.d/vm.conf /etc/apache2/sites-enabled/vm*conf
/etc/php/7.0/fpm/pool.d/vm.conf:listen = /var/php-fpm/php7.0-fpm-vm.sock
Using pipes instead of ports means that the fpm interface is not exposed to external networks, and that the permissions on the pipes can be enforced. Forcing it to ports breaks both of those security precautions.