So I am a Ph.D. student, I just finished my two 45-minutes virtual onsite interviews for Applied Research Scientist internship US office.
One of which was reseach / team match interview, the other was a techinichal interview.

I thought I did really well in both, the interviewer in the team match/research interview seemed happy and at the end he told me 'I actually learned many things from you today' so I thought it went well.

For the coding interview I was asked 2 questions, both of which I solved and the interviewer seemed happy as well and told me that he will give a positive review.

Yet, my reuciter emailed me that there's another follow-up team-match/ research interview (which I guess was not initally planned), I am not sure what went wrong ? is it maybe the interviewer thought I would be not good match overall ? or wont be a good match on his team? or are they filtering out candidates maybe ? I just really wish to know as it is making me a bit nervous, so I can prepare better for my follow up. Any insights on what might be the reason / meaning of the follow up interview?