Solution : https://service.sap.com/sap/support/notes/319867 (SAP Service marketplace login required)
Key words : 
deleting trfc/qrfc luws  319860, trfc/qrfc-luw  319814, basis support package, /3 support package, qrfc version 4, qrfc monitors  319681, error correction, blocking queue, status nosends  319616, poor performance
Related Notes : 
       
| 369007 | qRFC: Configuration for the QIN Scheduler | 
| 366869 | HOLD/EXECUTED/WCONFIRM entries in ARFCRSTATE | 
| 326617 | qRFC: ASSIGN_LENGTH_0 in LORFCU24 (SAPLORFC) | 
| 319685 | Determination of last function in tRFC/qRFC-LUW | 
| 166096 | qRFC installation for 3.xx, 4.0x, 4.5x and 4.6x |