This is so weird, happened to four users in my org in the last few days.
All are on Macs, bound to AD with mobile accounts.
AD account usernames are all first initial and last name (eg jdoe) but for some reason I'm getting reports that the usernames have changed to first name last name (eg. johndoe). I create these mobile accounts myself and send them to remote users. I've been doing it the same way or years so I'm totally confused as to how this could happen and no idea how to fix it.
Only way I have seen this happen in the field is if someone with admin privileges (Domain Admin) physically changing the DisplayName in Active Directory Users and Computers but that would not change the username those are usually difficult to to change you are better off deleting the entire profile and re-creating it for a new username at that point. Are you sure, your users are not getting confused with Display Names?
Sorry for my tardy response.
So yeah, I'm sure none of our domain admins have done anything. I've confirmed that the user name is incorrect via having them run a whoami on the commandline. I can also see the login name when I look at Computer Usage History in the Jamf portal.
Have a ticket open with Azure AD folks but they aren't really responding. I'm told there's a "backlog" (MS support has always sucked in my experience).