I passed the first online test and they sent me an email to let me book a time slot for the next step. And 3 hrs later they told me they will not continue for my candidate. I don't know what's going on

Initially I had 2 phone screens, one by a recruiter and another by an hr director. I was then called in for an interview. The interview started off with some general questions about my background and process of development. It lasted for almost an hour and had a variety of questions ranging from deployment and testing procedures to general questions such as "why do you want to work here?". Near the end of the interview they asked me whether I would be willing to come in for a technical interview. I think it's worth mentioning at this point that the 2 developers present vehemently expressed that they were well aware how unrealistic a whiteboard interview is and as such the procedure was merely to prod my understanding of the concepts in general. When I came in to the technical interview I was surprised to learn that the interview was not going to be done on a whiteboard, but instead with paper and pen in a closed room alone. This was certainly unique in my experience since the usual procedure was white boarding problems. The questions ranged from very simple, such as explain the difference between <p> and <div>, to simple algos such as FizzBuzz, then to more complex such problems such as overwriting Django methods, then finally to constructing and rotating a matrix. Writing these algos on a piece of paper was an incredibly awkward experience. At least with a whiteboard interview you get to explain what you are trying to achieve incase you forgot some library name or function name, but here you were just left to your own devices hoping that you had memorized every function name exactly.