PI interface message monitor data can not find in SXI_MONITOR

Hi PI Experts

    I have a question about PI message monitor.I call a PI method to send data out from SAP ECC 6.0 to PI server.

   But after i call it finished,sometimes i can find the interface message in T-code:SXI_MONITOR,but sometimes i can not find it in T-code:SXI_MONITOR

   Detail process code as below: after i call PI method complete,i put 'S' in variant zt_flag.and the i catch fault information in next step.

   The problem is: when zt_flag is 'S',why i can not find PI message data in T-code:SXI_MONITOR. Can anyone help me to answer this question?

    try.

       call method si_transform_order_out->si_transform_order_out

         exporting

           output = gt_out.

       commit work.

       zt_flag = 'S'.

     catch cx_ai_system_fault .

              create object fault.

       errortext = fault->errortext.

       zt_flag = 'F'.

   endtry.