When you perform an eDiscovery search in Exchange Server 2013 to export relevant content within many mailboxes, the search and export operation is unsuccessful. Additionally, you receive the following error message:
NotFound Export failed with error type: 'NotFound'.
Note This issue may not occur when you perform an eDiscovery search within one or two mailboxes.
This issue occurs if fetch ItemIds in the preparation stage are not performed in a timely manner. The error message occurs if some items are being changed (such as items being deleted or archived) before the fetch.