Solution : https://service.sap.com/sap/support/notes/441932 (SAP Service marketplace login required)
Key words : 
order <order number> item <item number> incorrect' appears, short text 'incorrect call', function group /sapapo/dm_boptree, function group /sapapo/dm_atptree, function group /sapapo/atp_update, function group /sapapo/dm_atptube, qrfc monitor transaction smq1, order item, 0 call transaction se37, call transaction se37
Related Notes : 
       
| 444641 | Correction of incorrect sales order requirements with APO | 
| 402484 | Backorder processing: Main item carries confirmed quantity | 
| 375193 | Backorder processing: Composite SAP note on posting |