HI,
Can you check if any services are configured to use the DA account ? I will suggest you to create a new account as a backup.
Check if there are any scheduled tasks such as backups, AV scanning or any tasks that is triggered by the activity and using this account. Process of elimination is required so consider all the options on the AD Domain Controller, do you have any clients that might be using this accuont? Disable any schedule tasks to start with.
Hope this helps.
JS
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