China’s economic slowdown has become a big problem for banks that serve the rich. 

For years, banks including Citigroup, JPMorgan and UBS competed hard to win business from China’s giant pool of wealthy people. They hired thousands of relationship managers with the language skills and cultural know-how to gain the trust of mainland China’s moneyed class, and helped them buy shares in Hong Kong, real estate in the U.S. and expensive paintings from European collections.