Office 365 Outlook sign-in keep appearing every time when I open

One of my domain users is very upset because of the outlook behavior. Whenever he opens the outlook its continually gets the Office 365 sign in box popping up and requiring him to sign in. After he signed in, outlook works fine before he close it, requires him to sign in again.

sometime is too much even pop up windows appears while he has been working in Outlook mean outlook is still open he didn’t closed or reopened it. I thought it cloud be some conflicts between his device to the exchange, but that could be because he gets signed out, hence the sign in box. His Internet connection is stable.

I have followed the below troubleshooting the following:

  • Checked that always require sign in check box is not checked in the profile settings
  • Removed the Office 365 entries in credential manager
  • Deleted the existing profile and created a new profile
  • Deleted the .OST file so it creates a new .OST, it did.
  • Quick and online repaired Office
  • Re-installed Office
  • Checking the remember me box does not work.

Any suggestions are greatly helpful