I’ve spent hours trying to figure out why an Outlook client kept prompting for a password when I moved the users mailbox to Exchange 2016. After hours of the normal troubleshooting I found that it did not prompt for the password when cached mode was off. After having the user connect to another machine for testing and comparing the Connection Status (Shit + right click Outlook icon in systray) I found that it wasn’t making a second connection to the Exchange Directory.
I closed Outlook, went to C:\users\username\appdata\microsoft\outlook and deleted the offlineaddressbook folder and re-opened Outlook. Whola it worked again!