So they told you that you passed the round but they did not give you any feedback about it, correct?
If so, according to my experience, I would avoid emailing your interviewers. They probably have extremely full agendas and won't have time anyways to answer your email.
I have done interviews for various consulting companies in Italy and it happened to me various time not to receive appropriate feedbacks between different rounds of interviews (even in MBBs).
If you really want to get a feedback, you could try again with HR by sending a gentle reminder. However, I would suggest you to work on self-evaluation in order to identify the weaknessess point of you past interviews (I am quite sure you can have a pretty good guess about them). You can then do some final work on those in order to get ready for your next round.
With you super good luck and happy to answer to other doubts if you need help!