We're doing some emergency API maintenance because we've actually outgrown our current storage system. We're trying to get the API working in the meantime by doing some maintenance, which should (hopefully!) improve logins.
We are working on a more permanent solution to replace the API that should hopefully be out sometime this week, but it isn't ready yet, and MCSG needs to work in the meantime! 
While we're doing this maintenance, you will likely see a "We are having unexpected issues" message when you try to log in. Don't panic; we're working on it!
UPDATE 1: Servers are back up for now. We will keep monitoring the API, and if needed, we will do more maintenance on it.
UPDATE 2: Everything's working again, surprisingly much better than before! Achievements and polls are disabled for the time being (it will appear as if you have all achievements right now, and a poll that says "Polls are disabled." will appear).
