Solution : https://service.sap.com/sap/support/notes/418102 (SAP Service marketplace login required)
Key words : 
additional key words lprio, scheduling agreements cross selling, attribute delivery priority, processing sales order, component type lprio, sales order processing, cross selling, field lprio, shipping scheduling, /3  apo processes
Related Notes : 
       
| 439778 | |
| 376933 | Delivr schedlg w/ APO:Addtnl flds INCO1,VSTEL,ROUTE | 
| 362109 | APO scheduling & conditions: fields filled from R/3 | 
| 322509 | APO integration of scheduling "Exit inserted" |