I had this exact issue on another machine, that after 2.5 hours on the phone with MS support (via Zoom), the solution was to uninstall MS Office 365 and reinstall it. Spent weeks with MS support and he got rather irritated when they told him to disable ADAL. He then started digging into Windows and how modern auth works and came across the above fix.

Microsoft Support and Recovery Assistant

I do NOT have this issue with the other laptop, an iPad, a MacBook Pro and tablet. But as soon as i log out and log back in, the plugin desactivates itself and the authentication bug comes back. Get a free trial to explore all the solution’s data protection capabilities. Domain verification issues can also prevent the normal use of the Microsoft Office 365 suite. Organizations value the capabilities that the Microsoft 365 suite provides for shared access and simultaneous file editing for team members.

Common Office 365 Issues and How to Solve Them

Use the NAKIVO solution to back up Microsoft 365 data in Exchange Online, Teams, OneDrive and SharePoint Online for uninterrupted workflows and zero downtime.

How to fix Office 365 issues related to synchronization

If multiple versions of Microsoft Office are installed, Office 365 activation issues may occur. Uninstall old versions of Microsoft Office from your computer and try to activate Microsoft Office 365 again. This works for a week and then the issue raises it’s head again.

Follow the instructions provided by the assistant to find and resolve Microsoft Office 365 problems.As soon as he figured it out he handed the full fix to MS support with all instructions as shown above.Domain verification issues can also prevent the normal use of the Microsoft Office 365 suite.If you are having a lot of end-user support headache because of Office365 quirkiness… well, it may very well be because this rather critical module is missing.Microsoft Support and Recovery Assistant can help you resolve problems with Microsoft Office, Office 365, and Outlook.You can disable Add-Ins on launch by pressing CTRL and hitting the Microsoft Office app shortcut.

Microsoft 365 Issues with the Safari Browser

The good news is that the majority of problems can easily be solved on the client’s side. Microsoft recommends updating Windows, Microsoft Office and other software regularly. Microsoft updates are released on a regular basis and allow you to protect software against known threats, fix bugs, and so on. Office 365 known issues are usually fixed by these updates. Let’s find out what you can do if updates are not installed automatically, and what factors can cause update issues. Reboot your system and try to launch your Outlook app after to check if the synchronization issues are solved.

How to fix Office 365 login issue?
Step-by-Step Troubleshooting for Microsoft Office 365 Login IssuesCheck if the caps lock is on.Make sure you are using the correct account (work, school, or personal).Double-check the username and password before entering.Ensure there is no extra space before or after your username and password.

Additional resources

Many issues that you may face day-to-day can be fixed on the client side. If you encounter an issue in Office 365 that can only be fixed by the vendor, Microsoft usually releases an update to resolve any known issues as soon as possible. This is now the 2nd machine that presents the same issue. I have a valid MS 365 subscription that includes 5 device licenses. I checked my MS account info page, subscription is fine.

Just today he IM’d me and said "oh yeah, this other issue we have been trying to fix for weeks on end… it was ALSO just resolved because we fixed this". My main concern is that these dialog boxes may return, prompting further user frustration and possibly generating tickets. Speaking of research, I haven’t found much info newer than December 2018. I haven’t opened a ticket with MS Office 365 login issues yet but I may if my search does not prove fruitful. Once the key is added, and the user restarts Outlook, they receive a legacy authentication dialog box, enter their domain password, and connect to their mailbox without issue. This seems to be our most effective fix, and it’s the one we arrived at after hours of forum digging and web searches.

You’d think after 10 years of O365 being used, the last thing you’d have issues with is Authentication… Yet here we are, same issue, different decade. If your Office 365 subscription has expired, buy a new license and extend your subscription for a new period. Or, any suggestion on how to fix this issue, even better.