Issue with MessageUID

Experts

We're working for a client and as one part of interfaces, IDoc is used to send data from ECC to MII system via message listener. Everything works fine till today something strange is found.

1. MATMAS (Standard IDoc) is used for downloading Material Master related data from ECC to MII.

2. A set of different material master data was sent at the same time from ECC

3. At MII Message Monitor, this is found that Received Time for couple of them, Message UID are all SAME, though the XML data (mainly Material Number (MATNR), Idoc number (DOCNUM) received are different.

Please see below

Can anyone highlight why this kind of issue (duplicate MessageUID for different IDoc data) is happening?

Regards

Som