Meta Research Scientist Intern interview questions

I applied one of reserach scientist internship at Meta, but it did not move forward at first time. But after a few months, HR told me to have an interview for that position. It was something weird. I took two interviews, one is for research background, and the other for live coding test. Research background interview went well in my opinion, but I could not complete the coding even though I explained all detailed algorithm for given problem. The interviewer always ask me a time complexity for the algorithms.