Some mainland Chinese investors who bought properties in Hong Kong at high prices several years ago have panicked amid souring sentiment and sold at big losses of up to HK$8.2 million.For instance, Xiao Yonghong and Sun Darui, the younger sister and brother-in-law of missing Chinese billionaire Xiao Jianhua – founder of the troubled Tomorrow Group – offloaded a 337 square foot retail unit at Causeway Place shopping centre for HK$18 million (US$2.29 million), incurring a loss of HK$8.23 million…