TOKYO—SoftBank Group Corp. said steeper-than-expected losses on office-share firm WeWork pushed its net loss for the latest fiscal year to around ¥900 billion ($8.4 billion)—$1.4 billion more than it announced just two weeks ago.

The Japanese tech conglomerate, best known for its $100 billion Vision Fund, is scrambling to calculate the hit to its bottom line from souring investments before it releases earnings on May 18 for the year ended March 31. The deeper loss comes from SoftBank’s multibillion-dollar rescue of We Co.,…

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