I was getting a 504 (IIRC) for a couple of domains that were something like "harmattan-dev" when I checked things out in the terminal...
They were the only two playing-up at the time, perhaps they're the appsformeego/C-OBS relevant ones, although I was sure they used a diff. domain/URL, night.

*EDIT*
Actually IIRC "harmattan-dev" are the dev mode repos....