Error: "Content Index State Failed" when auditing mailbox access on Exchange 2013

When auditing mailbox access on Exchange 2013, you receive the following error:

"Cannot audit mailboxes stored in the AAA database on the BBB server. The "Content Index State Failed" error has occurred on your Exchange server."

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Your Exchange server databases have unhealthy status "ContextIndexState:Failed".
As a result, Netwrix Auditor cannot collect audit data about mailboxes with the Search-MailboxAuditLog cmdlet.

To determine the exact database that has failed indexes, run the following command: Get-MailboxDatabaseCopyStatus
See Microsoft documentation for more information: https://technet.microsoft.com/en-us/library/dd298044%28v=exchg.150%29.aspx

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Rebuild failed indexes on your Exchange server side. See the Microsoft article "Reseed the search catalog" for more information: https://technet.microsoft.com/EN-US/library/ee633475(v=exchg.150).aspx

After fixing the failed indexes, restart data collection.