There was a report in VentureBeat as early as 3:30 a.m. ET saying that Teams users in Europe were experiencing major outages.
The outage comes at a bad time for the world economy as many white collar workers have been forced to work from home in order to limit exposure to the coronavirus.
It is not clear whether the increased number of users contributed to Monday's issues.
“We’ve taken steps to address an issue that a subset of our customers may have experienced," a Microsoft spokesperson told TheStreet. "Our engineering teams continue to actively monitor performance and usage trends."
At 5:17 AM, app's Twitter feed was responding to questions from users reporting issues with the service.
That message was repeated almost verbatim for the next two hours as multiple users mentioned issues with the service online.
The company later went on to say "We apologize for any inconvenience caused and thank you for your patience as we work towards a resolution. Please follow us on Twitter for further updates."
Microsoft Teams is seen as the biggest competitor to former Silicon Valley unicorn Slack (WORK) - Get Report, with Microsoft reporting inroads into the messaging space in recent weeks. In November, Microsoft announced that Teams had surpassed 20 million daily active users, extending its lead over Slack.
As of October, Slack had just over 12 million daily active users.
The entire market was down big Monday, with the S&P 500 sliding close to 9%, but Microsoft declined 10.3% while Slack fell 6.2%.
But Slack had its own recent connectivity issues last week, so the biggest loser lately may be the stuck-at-home office worker.