1 hour HackerRank assessment, then 2-3 interview stages with recruitment team, final interview stage would be in person at London office, stages leading up to that would be over video call

1st round: online interview with hackerrank leetcode medium followed by 2 math/probability questions; 1 easy standard bayes probability brain teaser, 1 harder problem that basically led to deriving the covariance of multinomial distribution (unless you know the formula). Very nice, professional interviewer with well structured interview format. 2nd round: phone interview. no structure to interview what so ever. free-flowing conversation discussing how you would go about analysing a dataset and extract pattern to perhaps predict stock price. very unprofessional interviewer, didnt have their camera on, Wasn't challenged intellectually at any point at all and mostly just questions like . e.g. "can you recall the OLS formula?". I guess they were testing if you have done any data cleaning/exploration/modelling before (and can you keep your cool infront of unprofessional interviewer) 3rd round: Another interview with absolutely no structure. Interviewer had nothing prepared for the interview and spent a few minutes to come up with (obviously not a well thought out/defined) problems to ask. Interviewer was very smart though and it turned into basically just an intellectual discussion of mathematical modelling problem on a topic that was unfamiliar to both of us. Interviewer was a nice person and very smart so it was enjoyable, but still it was unprofessional (e.g. they kept walking away from desk). Final round is onsite dataset interview that lasts the whole day. Waiting to schedule. Don't yet know what final round is like but for previous rounds, as you can see the interviews are a mess (except for round 1), and not problem-solving heavy compared to other firms. Possible I just got unlucky with the interviewers. Advice is to just keep your cool.