Its a shame you have been put in this situation. How frustrating. There have been 2-3 similar posts in the Q&A forum recently, so clearly their backend process is not slick.

My take would be to call the partner who referred you and get his guidance. HR must be swamped and they havent replied to you. So sending another chaser email wont be effective.

In parallel keep pursuing other options and dont rely too much on this current opportunity.

Hi there,

This is very confusing indeed.

Ultimately, you need to call HR. This is going to be very difficult to clear up via email!

Clarify and communicate with HR and the Partner until you have figured out what is going on. Thats the best you can do. Reminder emails, whatsapp messages, and even phone calls. HR are generally swamped people with lots of different streams going on - hence their delays in responding.

Hey,

not really sure if you already interviewed for the position you mentioned in the beginning as you are writing about invite only events afterwards.

"I have a partner who has referred me for one position at MBB. [...] I have attended all the events (invite-only events). [...] I got a rejection email [...] Even though I got the rejection email, I still got the invitation to an event (invite-only event)"

If you received a rejection for the position before interviewing and an invitation to a recruiting event, please take into account that there are plenty of reasons for such an rejection that a not tied to you personally (e.g. found an internal candidate, withdrew the job posting, ...). 

However I would recommend to use the in-person event in the office to build up a personal relation with HR and for sure also try to reach them via phone / mail or the partner beforehands to sort this out :)

Hope that helps,
Simon