Exponent Associate interview questions

This is fresh. I just received a rejection call this morning. The interview process itself was quite interesting. I just interviewed mid of January, 2024 at the Chicago office (Materials and Corrosion practice team), and got the rejection 3 days after. From the start, I sensed from the manager's body language that I might not be selected for the job, however I couldn't pinpoint what was wrong, but I still gave it my best effort. about 6 one on ones and a 45 minutes technical presentation. In my rejection call, the manager mentioned I couldn't really answer some fundamental questions which I believe were some questions on the stress state of beams under loading. (mechanical stuff - something I did in undergrad) Overall, I would say that the workplace seemed quite relaxed and everyone was very welcoming. It's the kind of environment where I think anyone would be happy to work. My main concern is the mental toll this experience took on me, particularly knowing that I might have been rejected right from the very beginning.