Solution : https://service.sap.com/sap/support/notes/137703 (SAP Service marketplace login required)
Key words : 
additional key words pos inbound, processed idocs decreases continuously, increasing program runtime, store goods receipt, processed sequentially, type wpuwbw01, report rbdapp01, problem occurs, stored temporarily, initialized explicitly
Related Notes : 
       
| 116784 | Performance improvement for the POS inbound | 
| 98393 | MB01: Incorrect value for pricing type '5' |