Just updated to 15.11.0 and immediately got this issue, where Outlook will keep asking for my Exchange password at random intervals (sometimes several times within a minute).
I cleared the 'Exchange' entries in Keychain Access, to no avail.
Upon closer inspection it looks like Outlook is actively overwriting the password value in the Keychain Access entry with a blank value... But I don't know what triggers it.
Is anyone facing the same issue?