Hi Masa,
Please find below comments for your questions.
Regarding user name issue,
+ What is the user name at right top of launchpad? - Employee First Name & Last Name
+ What is approve/reject comment history when you approve in MM SAPGUI transaction? - Comment history is manual - When manager enters comment for header level, he/she goes to header level and enters comment. If it is item level, then they enter at item level.
+ Have you maintained first name last name in the Gateway server? - Yes, we have maintained First name & Last name
Regards,
S.Srikanth