Solution : https://service.sap.com/sap/support/notes/418767 (SAP Service marketplace login required)
Key words : 
sales order remains unconfirmed, sales order remain unconfirmed, dynamic assembly processing, sales order, dynamic assembly, planned order, production order, bom exists, end product, receipt element
Related Notes : 
       
| 450154 | Dynamic assembly: Assembly order cannot be adjusted | 
| 434532 | Dynamic assembly: Runtime for control of configuration |