There are failed actions with 'An item with the same key has already been added' error message in Legal Processing 'Action' table while processing data using Legal Review Collector.
Missing [IgnoredFields] key parameters in the configuration of Legal Review Collector for the Matter.
Update the 'ZyLAB.EDiscovery.Collectors.LegalReview.dll.xml' config file for the Matter which is located in the '\MatterID\Assemblies\ZyLAB.EDiscovery.Collectors.LegalReview\' folder and where MatterID is the Matter number in Legal Processing, with 2 additional fields under the <Items> of the <IgnoredFields> section:
<Field name="IndexingErrorCode" />
<Field name="IndexingErrorMessage" />
The same update should be made to the 'ZyLAB.EDiscovery.Collectors.LegalReview.dll.xml' config file in the '\Program Files (x86)\ZyLAB\EDiscovery\Ediscoveryservice\Assemblies\Performers' folder, so future Matters will have the corrected configuration.