Unable to open Workflow Task on target after migration (4277225)

After a site copy completed and checking Workflow Tasks on the target environment some tasks fail to open with the error reported in SharePoint ULS log:

Logging Correlation Data Name=Request (GET:)
Logging Correlation Data Site=/
Publishing Setting [Display] as the FormContext.FormMode for the current page
Runtime System.ArgumentNullException: Value cannot be null.
   at Microsoft.SharePoint.Workflow.SPWorkflow.retrieveSchema(Schema schemaIndex)
   at Microsoft.SharePoint.Workflow.SPWorkflow.retrieveSchemaGuid(Schema schemaIndex)
   at Microsoft.SharePoint.Workflow.SPWorkflow.get_AssociationId()
   at Microsoft.SharePoint.Workflow.SPWorkflow.GetReadOnlyParentAssociation()
   at Microsoft.SharePoint.Workflow.SPWorkflow.get_ParentAssociation()
   at Microsoft.Office.Workflow.WrkTaskIPPage.OnLoad(EventArgs ea)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
Monitoring Leaving Monitored Scope (Request (GET:)). Execution Time=57.8665724275013

This error is caused by the user copying functionality. When users are no longer in Active Directory, the authorship metadata and user fields used by the Workflow Task are substituted by the migration account or left blank.

To retain the functionality of the Workflow Tasks, the deleted users must be copied to the target by utilizing the "Allow copying of deleted Active Directory users" option within the Copy Configuration Dialog. However, this option is only available for selection if Content Matrix is able to write data directly to the database, which is not supported by Microsoft and, if used, will impact your Microsoft warranty. For instructions on how to do so, click here.

Note: Make sure to enable the Advanced Mode on the Settings tab of the Content Matrix Console or on the job configuration window to see all the job configuration options.