SoftBank Group Corp is planning to cut headcount at its flagship Vision Fund investing arm, CEO Masayoshi Son said on Monday, after a crash in the value of its portfolio pushed his conglomerate to a record quarterly net loss. Vision Fund, which upended the world of venture capital with splashy bets on startups such as ridehailers Uber and Didi, posted a $23.1 billion loss in the April-June quarter as value evaporated from its investments in the market rout.