Hi,
this is correct for the field 'Container ID' on the Event Messages tab. Therefore you should check if the extraciton on TM side is working correctly. Either debug the extraction function module for the expected events or debug BAPI /SAPTRX/BAPI_EH_POST on EM side (MILESTONEDATA) to check the extracted data. Once you have done this you know if the issue is on TM side (extraction) or on EM side.
Maybe you can also double check the following as first step: Check the expected event profile (TA /SAPTRX/TSC0EE) you are using. For each expected event for which you want to use the fields DATA CS and DATA ID you have to UNCHECK the flag 'Do Not Set' in the line 'Data Function' - otherwise field DATA ID is not getting populated on EM side for the expected events. This is described in chapter 'Create new expected event profile' in the SCN document.
Best regards, Daniel