Account lockout policy issue

You know the answer. Create a test OU, link that particular policy, add the user in that OU and test it and see what difference you will see.

Was there any change happened in your environment?
Was this working before? Or is the first time you are testing it?

What happens if the test account gets a domain admin privilege and then test it with enabled linked policy?

You can also use Account Lockout Status tool and keep this handy. Choose the domain and the name of the user to see the status of the user's account.

If this falls again then go ahead and check with the application vendor. I am not sure which application and how the users are logging in.

Let me know if anything else is required.

Good Luck..!!
~SG~

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What's the better way to test this?  Create test users and put into test OU or need test Security Groups? I think OU is easier to put test users there/ Not sure if possible to link that policy into that OU.
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Easier to test by isolating the external users and putting the "external test" users in a different OU. And yes - you can apply GPO to an OU. But the first thing you should check is your account policy. You should also be looking at the authentication. Something's gotta be failing somewhere for the accounts to lockout. I'm thinking it could be a kerberos issue.

Correct. This is what I understand.  The account lockout policy cannot be applied to a separate OU. However, even after testing successfully on test Domain I don't feel comfortable enabling on Production Domain.  
I am thinking implementing granularity by Security Group. Users in the Security Group will be enabled.  Does that sound good?

If that's the case, I am waiting for the solution..!!

Interesting..!!

This is what I am thinking about.  Run the script every hour that would put those users in the group.