Symptoms

Using the Get Documents Metadata method and setting two filter properties. Recursive = true and a date field. Documents are in folders. Service Tester returns the proper items. In the workflow, the properties in the email are rendered as System.Stringn]. Not the values themselves. It works fine if the document is not in folder.
 

Diagnoses

Issue was reproduced in a test environment. Setting the recursive parameter to true means to get all documents in the document library. The Item reference is returning all documents in the library (document not in folder and inside folders) but it is returning the wrong property for the document - returned System.Stringt], but the document ID is returned correctly.
 

Resolution

Logged a bug regarding the issue. Workaround is before the email event, add a SmartObject Event, call the Document SMO Get Document Metadata by ID method, set ID to Item.ID, and map the outputs that you wanted to process data fields. Finally, use the process data fields on the email event.