As Leopold Aschenbrenner’s US hedge fund saw assets wiped off by more than two-thirds in a single month, some of China’s new portfolio managers also felt the shock across the Pacific, learning bitter lessons early in their careers. The 50-day market turmoil, sparked by a global correction in artificial intelligence stocks in June, turned some of China’s rookie managers into an unwitting focal point. Even seasoned investors faced hard questions from clients as portfolios sagged. For Yuan Zeqiang,...