You can follow along here to troubleshoot.
http://woshub.com/troubleshooting-identify-source-of-active-directory-account-lockouts/
--please don't forget to Accept as answer if the reply is helpful--
Regards, Dave Patrick ....
Microsoft Certified Professional
Microsoft MVP [Windows Server] Datacenter Management
Disclaimer: This posting is provided "AS IS" with no warranties or guarantees, and confers no rights.