I experience the issue myself as well, every once in a while. Tried CC cleaner to clean up registry and everything -- also keep in mind this disable faulty add-ins in Outlook is a fairly recent reinstall of windows. I am unable to stay signed in to my work account on Teams, Outlook, Office365 for more than 5 minutes.

Outlook credential prompt loop

I disabled the Zoom and Adobe PDF plugins and it stopped prompting me immediately. My client’s Outlook will only continuously ask for the password Outlook OST vs PST repair after MFA is enforced and Office.com has been logged in. It would be nice if it distinguished between your password and the app password. You may have to rebuild/restore your outlook folder/files which is a pain. I’d do that one step at a time, forgoing the restore of the cached files. Not sure if it has to do with being an onmicrosoft.com account that has no domain assigned to it.

Loop of 'Sign in to your account'.

We had the issue where Outlook 2016 kept prompting for a password for an Office 365 user whose laptop was connected to their Office 365 account using Windows 10 Pro. The repeated issue logging in started after I enabled the modern authentication in the Office 365 administration panel. The user could use the Windows mail and calendar apps but Outlook wouldn’t connect and kept prompting for a password. Checking the Account in Word showed the correct authentication and subscription.

Resetting the Windows Credential Manager:

I have contacted my organization and everything looks alright from their end.. I went as far as getting a new device but it did not cut it. When I try to sign again it will be stuck in sign in loop with the message " Taking you to your organization sign in page" after I have logged in on my company site... When I log in to my account at first from a new device or after a while, it stays signed in and I can work peacefully for about an hour, then it automatically signs me out. Or, any suggestion on how to fix this issue, even repair corrupted OST in Outlook better. I do NOT have this issue with the other laptop, an iPad, a MacBook Pro and tablet.

• Unfortunately when the problem occurs they’ve asked us to ring straight away but of course you can never get them instantly (we’ve just been given someone’s direct number now).
• I feel like this issue is getting progressively worse as the fix used to be clearing the credential manager or if it was bad uninstalling the entire Office Suite, clearing all traces and reinstalling and now we are seeing nothing helping it.
• This is now the 2nd machine that presents the same issue.
• I disabled the Zoom and Adobe PDF plugins and it stopped prompting me immediately.
• Clear the Windows Credential manager or recreate the users Outlook profile.
• On the main machine where I have been using the suite, now my account is deactivated and if I try to authenticate, it looks like it works but then get the "Fix", "Authenticate", "Activate" or "Resolve" buttons, all of which do nothing.

Changing Outlook Security Settings:

If this box is greyed out or disabled then you need to reset the Windows Credential Manager first. @Microsoft, given the level of attention the community has given this issue, I hope you come up with an update soon. We have been experiencing the exact same issue for months now.