Exchange owa opens wrong mailbox

Joakim Silverdrake 

I understand that after changing from Forms Based Authentication to Windows Integrated on Exchange owa and ecp, user(s) begin to experience sign-in issues like Outlook Web Access Opening the wrong Mailbox.

You confirmed that when you revert back to the Forms Based Authentication, issue stops happening. Can I know the URL user(s) log in to OWA with? Can user(s) try accessing Outlook on the web using the link https://<ServerName>/owa and ensure affected users are using the supported web browsers.

The Supported Web browsers for Outlook on the web in Exchange 2019 are Microsoft Edge, Internet Explorer 11, and the most recent versions of Mozilla Firefox, Google Chrome, and Apple Safari.

Lastly, confirm if issues occur when on the incognito mode browsers as well. Feel free to reach out to me if you need further assistance. Thank you!