New Delhi, Nov. 13 -- Microsoft Outlook went dark on Rita Elkazzi just as a volatile week in markets was coming to an end. As swings in AI stocks and bonds kept traders on edge, the UBS Group AG execution-sales head for Australia and New Zealand was forced onto phones and alternative channels to communicate.

"It's been a bit of a disaster and I can't believe still not resolved," said Sydney-based Elkazzi. "It means a lot more diligence on ensuring trade recaps et cetera are accurate."

Elkazzi's experience is echoed by many after Microsoft Corp. suffered one of its most severe disruptions in recent memory. The tech giant is still struggling to restore access to some of its flagship software hours after an outage began, affecting its Outl...