Had this exact issue (no logging on 500 error), where you are
wondering "what in the world just happened to my app" when I did a
passenger update two weeks ago (I've just resolved it). The best
advice I was given (which solved things for me quickly) was to make
SURE your connection to the db is working properly from rails.
Installing phpmyadmin may have messed with user premissions or
whatnot, so that's what I'd start debugging. When my issue came up I
assumed it was Passenger, but it was actually a bad socket path for my
production setup in database.yml, which I happened to update at the
same time I upgraded Passenger. Hope any of this helps.
BJ Neilsen