I found something really weird today. An on-prem user changed their Windows AD password a couple of weeks ago, and since then every day when they log in and open Outlook their account locks. I unlock, then they can get into Outlook and work for the rest of the day with no problems. I tried resetting thei Outlook profile and almost was going to reset their Windows profile (which would have fixed it apparently), but I googled and found that there is something called the “Windows Credential Manager” in the control panel. Sure enough this had an old password stored in it, so I just cleared taht out and Outlook was happy again. Weird.