Happens all the time. You would boot to Recovery and reset the password:
If you can't reset your Mac login password - Apple Support
if you have FileVault enabled, you will need the Personal Recovery Key. We have our users reset their password to their current organization password.
Long dead thread here that I began.
However, I encountered this same issue again and found a pretty intuitive workaround. Disable wireless, sign in as the local admin, change the password in Active Directory for the user in question, then in users and groups (as the local admin) change the users password to what it was newly set as in Active Directory. Sign out of the admin, re-enable wireless, then sign in as the user and it resolves the password synchronization issue.