I do the "not logged in" test now regularly when I get a 504 with my autologon browser. Today there was a clear difference, the session with autologon getting 504's and the session without autologon showing the forum.
That sounds like not-logged-in pages might be cacheable, but when you’re logged in, it has to hit the database for the extra information you get. If that database is overloaded (or crashes), that could explain the regular dead forums.
I hope no one has to restore the database manually every time.
