Meta Research Scientist I interview questions

A recruiter reached out to me. I had one screening interview that went well. After the interview, recruiter asked me to fill out a form about my immigration status (I was on a student visa with 2+ years of work authorization after my graduation). After that they asked me to fill out an additional questionnaire tailored for O-1 visa. All this legal back and forth took approximately a week. After that I got rejected without any explanation of the reasons.

1 Phone Screen 6 rounds VO: - Research presentation; - Statistics; - ML coding; - ML design; - Leetcoding; - BQ. 45 - 60 min each round. Strong statistics knowledge is required. Most interviewers are Stat PhD.