The International Monetary Fund called the German bank the riskiest financial institution in the world as a potential source of external shocks to the financial system. That labeling came right after a U.S. banking unit of Deutsche Bank was one of just two banks to fail the Federal Reserve’s “stress test,” an exercise measuring how 33 banks would fare in the event of another financial crisis. The IMF report helped send the bank’s stock Thursday to its lowest price in more than 30 years, as shares already were reeling from the U.K.’s vote to leave the European Union. Deutsche Bank, Germany’s biggest lender, is struggling to return to full-year profitability amid an overhaul to boost capital cushions and cut jobs and expenses. The potential financial and economic upheaval from the Brexit vote could further complicate the bank’s efforts to sell assets and stabilize its core businesses.