Re-checking the Virtualmin configuration on a fresh CentOS 7.x Virtualmin setup gives the error:
The plugin DAV Login cannot be used : The Apache mod_dav module must be installed before DAV can be used
Checking it with
httpd -M | grep dav gives no output, so it is indeed missing.
In fact, we do not use dav at all, so I just disabled the
DAV Login on Features and Plugins page and this time I have clean Virtualmin re-check validation. However, the issue should be addressed anyway.