Outlook asks for password continually

There are a number of reasons for this. First I would look inside the Office 365 admin portal to make sure your password expiration policy is not set to only a few days

https://docs.microsoft.com/en-gb/office365/admin/manage/set-password-expiration-policy?redirectSourc...

If this is ok, setting the below registry key to 1 in below path often resolves it

Path: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity

Key: DisableADALatopWAMOverride (DWORD)

https://office365.uservoice.com/forums/264636-general/suggestions/32694751-outlook-is-not-syncing-an...

I would try that on a single user to see if it works before rolling it out. If that doesn't work let us know.