Civstats is back up again. (Game was up but forgot to reactivate civstats - sorry).
Something is definitely up though - the game 'hung' again on sunday. Same problem as before where something seems to get corrupted. It was still allowing everyone to connect and play their turns, but the admin interface was frozen, and reloading from autosaves gives the exact same behaviour (even after a reboot) forcing a reload from an earlier autosave. This time it seems to have gone wrong sometime between Ricardo's login and Ras' login.
I'm going to have to start checking it every day now (since we can't rely on civstats or login problems to catch it). I don't think it's the server hardware as it's been running another game in parallel without any problems on the other game, and it has run much bigger maps than this one in the past. If anyone has any ideas or spots anything odd while playing, please let me know though.
We might also try switching back to port 2056 at some point in case that makes any difference (although, I doubt it).
Anyway - everything is back up and running fine again now.