SXMB_MONI - Message Life Cycle. Data Sent information

Hi,

I have an inbound synchronous interface scenario from third party system to the S/4 HANA system. The interface is processed with SAP PO 7.5 as the middle ware and sent to S/4 HANA via ABAP proxy. Then third party complaining a time out error causing the document is created in S/4 HANA but they have closed the connection.

So I check the message in SXMB_MONI (we have turned on the LOGGING_SYNC therefore successful synchronous messages are also logged). And check the message life cycle and found the information as below:

Here, what does the Data Sent information mean? Does it mean the data sent from the third party system? Notice that there is a 2 mins interval between data sent and the execute from time. Where could this slowness could be? In SAP PO processing? I believe the processing in S/4 HANA is only 24 seconds.

Thank you.