Exa Corporation interview questions

The interview process was surprisingly slow (+1.5 month) and continued up to 3 weeks after the proposed start date of the internship. I am calling it slow as they were really in a hurry to hire someone. We initially went through a phone screening followed by an hour WebEx meeting (to +12 engineers), where I was asked to give a presentation of my relevant work experience. I was later asked to provide 3-4 references who are familiar with my work. I later found out that the company has reached out to all 4 references that I provided, which was really surprising that they went through all that effort for a temporary intern position. I was called a week later without notice by a manager who had missed my WebEx presentation and was interviewed through the phone call. Later that day, I once again was called and told that the engineering team is super impressed with my qualifications and I should expect to hear from the HR in the following week to finalize the start date. I also made some requests about the timing and duration of the internship and they were truly flexible (I was unofficially offered the position). However, I never heard back from the HR but the same manager who last interviewed me called at some strange time, just thanked me for my interest in the company and said they are moving on with other candidates. They wasted a lot of time with interviewing for a temporary intern position and more importantly they wasted a lot of my time with offering the position and then withdrawing it with no apparent good reason!

Two rounds of interview. First round is a group interview with 3-4 interviewer present. More soft skill questions. Questions about academic and previous work experience. Second round technical and normally interview is taken by the technical director. Solving problems in aerodynamics using fundamental concepts.