Fresh install. Virtualmin version 6.04. Ubuntu server 16.04. I installed a domain and two sub servers. The both worked. I then configured the system to serve svn using the instructions at https://tecadmin.net/install-subversion-server-on-ubuntu/. Now the only thing that works is svn. Any other attempt to access the system via http or https gets the above error. I removed all the changes I made to the system (as far as I can tell) and it still fails. Yes I restarted apache. sub1.server.com sub2.server.com and server.com all give the same error.
I experienced the exact same error a few days ago with a system behind a NAT firewall and thought that was causing it, so i spun up a VPS and am experiencing the same issue. Nothing in any error log I can find.