Update: The situation is improving with the Microsoft 365 outage. Access has returned to most users, but we have not received an official report from Microsoft. I will send a final update once the outage is resolved.
Original: Microsoft has identified an issue with users accessing and viewing web apps in Microsoft 365 at 6:30 PM on April 19. Microsoft has identified the initial cause and is working to repair the issue. At this time, individuals may be unable to access web apps for Microsoft 365, such as Excel Online, Word Online, Sharepoint Online, Planner, Outlook Online or other web-based versions of Microsoft Office applications. Locally installed applications, such as the desktop versions of Office, are working properly at this time. We are monitoring the situation.