Solution : https://service.sap.com/sap/support/notes/1378291 (SAP Service marketplace login required)
Key words : 
meta data processing takes time, terms po history, relevant support package, parallel processing, process performance, purchase order, caused due, programming error, solution implement, correction instructions
Related Notes : 
       
| 1378344 | Performance improvement in PO check | 
| 1266771 | SRM 7.0 Performance Guide |