This really falls in the category of wild speculation, but my partner used to work in the hedge fund business and it still tapped into the community, and apparently there's some speculation that Deutsche Bank may be close to failing and that the reason bond yields were going UP last week was the possibility they were cashing out their bond holdings to get liquidity now and that the Fed stepped in to buy when DB was flooding the market and not finding enough buyers. One of the Swiss Banks is also apparently on the brink and may be/have been doing the same.
(And if you're really into conspiracy theories, apparently Trump, who has a well documented history of borrowing from DB, was screaming at Mnuchin to have the Fed do something the night before the Fed intervened. If DB goes into receivership, then the German government will possess all of its records and the lawsuit currently pending before SCOTUS about DB subpoenas would be moot should its books be made public in receivership.)
(And if you're really into conspiracy theories, apparently Trump, who has a well documented history of borrowing from DB, was screaming at Mnuchin to have the Fed do something the night before the Fed intervened. If DB goes into receivership, then the German government will possess all of its records and the lawsuit currently pending before SCOTUS about DB subpoenas would be moot should its books be made public in receivership.)