Solution : https://service.sap.com/sap/support/notes/385599 (SAP Service marketplace login required)
Key words : 
source code correctionsthe includes /sapapo/lbop_bufferfr2, 'discard multi-level atp check, additional key words transaction, screen enter /sapapo/rrp_atp, attached source code, call transaction se37, planning orders created, 'initialized global memory, enter /sapapo/rrp_bop_new_luw, enter /sapapo/rrp_bop_multilvl_kill
Related Notes : 
       
| 420605 | Composite SAP Note for BOP performance in APO 3.0A | 
| 388894 | Backorder processing with manufacturing | 
| 385761 | CTP: Error in configuration changes | 
| 384187 | Backorder processing: Planned orders not saved | 
| 375193 | Backorder processing: Composite SAP note on posting |