Solution : https://service.sap.com/sap/support/notes/495171 (SAP Service marketplace login required)
Key words : 
changed sales order items, sales order update, sales order item, backorder processing run, requested delivery date, request schedule line, confirmation schedule line, cif queues hang, /sapapo/bop_update reason, /sapapo/bop
Related Notes : 
       
| 493656 | Sales order items not updated in the OLTP system | 
| 480839 | Ignore requirement change due to incorrect object ref. query | 
| 456543 | APO BOP: incorrect results due to missing object reference | 
| 375193 | Backorder processing: Composite SAP note on posting |