Ok, so this has been broken in the charm for a while. The package shipped vhost should be disabled by the charm but due to a bug that is not happening.
However xenial and zesty both seem to allow apache to start when it has a conflicting port with haproxy. If haproxy is running and bound to 8776 on both ipv4 and ipv6 then apache starts and creates a duplicate bind to 8776 on the ipv6 address. Bug #1720378
Ok, so this has been broken in the charm for a while. The package shipped vhost should be disabled by the charm but due to a bug that is not happening.
However xenial and zesty both seem to allow apache to start when it has a conflicting port with haproxy. If haproxy is running and bound to 8776 on both ipv4 and ipv6 then apache starts and creates a duplicate bind to 8776 on the ipv6 address. Bug #1720378