having the same exact issue on all 3 of my email accounts to O365. all starting at around 5a today. I've tried rotating the app password on one of the accounts with no success. I'm not sure if this is on the MS side or not... but thought I'd throw out a "me too" while I investigate and troubleshoot.
v1.14.1
Web Server Software Apache
MySQL Version 5.7.29
PHP Version 7.2.24-0ubuntu0.18.04.4