metrics.torproject.org graphs not showing up (png is a 500 error)

On each of the metrics.torproject.org pages that is supposed to have a graph, e.g. https://metrics.torproject.org/bandwidth.html there is no graph.

@trinity-1686a debugged a bit and said: the supposed png returns an html file stating "Oops! Something went wrong here! We encountered a 500 Internal Server Error when processing your request!"

It sounds like some back-end service is busted?