Solution : https://service.sap.com/sap/support/notes/314549 (SAP Service marketplace login required)
Key words : 
system generates message co630 'distribution rule, additional key words va01, sales order item triggers, set indicator 'coll, prerequisites solution implement, lower-level order, sales order, collective order, order type, assembly processing
Related Notes : 
       
| 440912 | Settlement rule after extending subnetwork | 
| 318747 | CO630 for assembly with collective order |