Winton Capital Management and Cantab Capital Partners, two U.K. computer-driven hedge funds, posted losses last month as global markets were rattled by concerns that China’s economy is faltering. Winton lost an estimated 4.3 percent in August in its $11.8 billion Winton Futures Fund, the worst month since July 2008, according to a letter sent to investors. Cantab erased gains for the year in its $2.6 billion CCP Quantitative strategy after...