TOKYO—SoftBank Group Corp. sank into red ink for the July-September period, dragged down by losses on its investments in China, the Japanese technology conglomerate said Monday. SoftBank reported a 397.9 billion yen ($3.5 billion) loss for the fiscal second quarter, compared to a 627 billion yen profit recorded the same period the previous year. Quarterly sales grew 11 percent to 1.5 trillion yen ($13 billion). Tokyo- based SoftBank said its investment portfolio called Vision Fund suffered losses, including the value of its stake in South Korean online retailer Coupang. But it said it booked gains on its shares in DoorDash, an online food-ordering service based in San Francisco. SoftBank said the recent crackdown in China on the technology sector weighed on Chinese share prices. SoftBank’s Vision Fund was hit by a 1 trillion yen ($9 billion) loss in the July-September quarter, according to its chief executive, Masayoshi Son. Son, who …