Last Thursday, as his company booked a $3.8 billion gain from its stake in Uber Technologies Inc., Masayoshi Son told SoftBank Group Corp. investors that their time had finally come. Instead, they're still waiting.

The day after Son's earnings presentation, SoftBank slid 5.4 percent and fell again Monday, dropping as much as 4.9 percent. Uber's initial public offering was a flop, with shares sliding on the first day of trading, at the same time the U.S. and China escalated tensions over their trade dispute.

SoftBank has lost about $9 billion in market value despite reporting last week that profit more than tripled thanks to the valuation gain from its stake in the U.S. ride-hailing giant.