Chinese authorities told the nation’s biggest state-owned firms and banks to start a fresh round of checks on their financial exposure and other links to Ant Group Co., renewing scrutiny of billionaire Jack Ma’s financial empire, according to people familiar with the matter. Multiple regulators, including the banking watchdog, recently told institutions under their oversight to closely examine all exposure they had to Ant, its subsidiaries and even its shareholders up to January, said the people, asking not to be identified as the matter is private. Those people described this as by far the most thorough and wide-ranging look into...