At some point, either a windows update or WAC update seems to have caused our WAC to not open 443 when running as the default Network Service account. If I change the service account to my administrative user account, it runs fine / launches fine.
I launched proc mon and did find that it randomly was denying that account access to a few spots under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates in the registry, so I added those permissions - but it didn't resolve the issue. No other 'access is denied' events occur in a proc mon when starting the service; the service 'starts' and doesn't end/stop/fail, it just doesn't open the port / the site is unavailable locally and via the network.
I can't find any log files to help troubleshoot, and would rather not use a service account as - i believe - updates will re-set the service to run on Network Service