Personally, I would have installed mailman elsewhere … MiaB servers are meant to be Miab Servers. I don’t like to make unsupported modifications.
If, however, I were to install mailman on the same server I certainly think that I would have changed the default document root.
Will you share the contents of the Server Block (vHost) file for lists.ecovillage.cc please? I am not great with them, but it seems pretty obvious that something has gone tilt there. Someone better than me will come along and they will need to see it anyways.