I don't know for sure what the original problem was, but the most recent issue was a result of implementing a new badge without rebuilding the API. Once the API was pushed to production, the bug was resolved. If it happens again (especially if there's a new badge) please let me (or really any employee) know. We can contact a developer directly.
From a comment on a related question:
Fundamentally the problem is that the API can remain broken without us really paying attention to it. I appreciate your report since it prompted us to rebuild the API. (That was the immediate problem this time around.) But we shouldn't really be relying on user reports for this sort of thing.
We need to start treating our products as a platform. We don't treat our API as mission critical. There's good reasons for that, but it's going to hurt us if we don't sort it out eventually. (Summary: sorry about that. We can do better.)
