Solution : https://service.sap.com/sap/support/notes/1474308 (SAP Service marketplace login required)
Key words :
reassigned user tasks list, fnd fix error, group reassigns, create task, reassigning
Related Notes :
| 1474307 | Task reassigned from same DL are not delivered to SharePoint |
| 1465331 | Duet Enterprise 1.0 Workflow Information Note |