Same as many people describe already. Serial process you can only move forward if you completed the last interview. I had 4 coding rounds, 3 leetcode, 1 React and a HM interview. I did well on 3 of the coding rounds, however on one of them the interviewer gave almost no description or example input or output. Most of the interviewers were very helpful. The final HM interview I was asked a problem about probability, which I bombed having no background in statistics or any context for this kind of thinking which is more math related. Overall the experience was good but if a candidate passes 3 coding why is the hiring manager asking more coding? I would have preferred system design...in any case there is usually one interviewer that sinks the entire effort...unfortunately in this case I think it was the hiring manager.