Something mysterious rattled one of the world’s most stable financial markets for 12 harrowing minutes on Oct. 15, 2014.During that brief window, the yield on the 10-year Treasury note—a benchmark security critical to funding the federal government—dropped dramatically and then surged, and no one could tell why. It was, said JPMorgan Chase CEO Jamie Dimon, “an event that is supposed to happen only once in every 3 billion years.