We are also seeing this in our organization. So far tested, Outlook for Mac, and Outlook for iOS has the issue. Outlook web does not. Microsoft Support replied that "it looks like the issue if from the server side. You will have to contact IT admin of your organization, who manage your account. They would be able to rectify the issue and help you on this". I will see if our IT is seeing anything from their end...
I let Microsoft Support know about other organizations having this issue today, as well