Solution : https://service.sap.com/sap/support/notes/423088 (SAP Service marketplace login required)
Key words : 
system frequently calls pricing, additional key words vf01, considerable runtime problems, pro-forma invoices, program error due, attached program correction, normal billing documents, header condition screen, billing document, header screens
Related Notes : 
       
| 557665 | |
| 457007 | |
| 436488 | |
| 379146 | |
| 118743 | Collective note performance in SD |