We noticed that we are constantly asked to login over and over again with version 16.3.6474.
We have reports from users than every 2-3 calendar entries in web mail they are asked to log back in. They just bought a brand new computer and have tried under Edge and Chrome.
We have also noticed logged in as an administrator. If we go to manage a domain, that we are asked to log in every few minutes.
If we stay on the spool screen and leave it for hours it seems fine. It is only when we leave the main screen.