Chinese authorities have asked the country’s largest state-owned companies and banks to begin a new round of checks on their financial exposure and other ties to Ant Group Co., renewing scrutiny of billionaire Jack Ma’s financial empire, according to people familiar with the matter. Several regulators, including the banking watchdog, recently asked the institutions under their watch to take a hard look at any exposure they had to Ant, its subsidiaries and even its shareholders through January, the people said, asking not to be identified as the matter is private. These people described this as by far the most thorough...