Using classic Outlook for Windows in business environments
11:45 EST 31-Jan. iOS MS OUTLOOK 2016 (i.e., "personal") I logged on successfully and have stayed logged on for 45 minutes. So far so good.
Logon was squirrelly: the app would not accept my password, and kept prompting me to re-enter it (same user experience as during the problem period), but in the meantime the app logged on with my (same) stored password in the background, so while it was prompting me to re-enter my password, it showed me connected and emails starting loading.
In the end, all is (currently) well.