Flux Federation interview questions

Three stage interview process. First a generic get-to-know-you type one, was quite positive and promising. Second was an 'show your thought process' problem based interview. Again, quite positive and gave me some insight into the types of problems they face. I find these interviews a bit of a cop out - they've already faced the problem and now want to test someone with zero knowledge of the company's ways of doing things to see if they could have done it better. Nevertheless I made it through to the third interview, which traditionally I have found is more of a culture fit interview. Not this one. It was an absolute grilling from one of the senior leaders, and felt like a test in the sense that they wanted specific answers to very philosophical questions. I felt they weren't looking to learn about me, my experiences or methods, they were looking for someone who thinks the same way they do. I walked away from it feeling very confused and somewhat upset - I've never been uncomfortable in an interview before but this was just plain awkward. This feeling must have been reciprocal as I received a generic unsuccessful message shortly after.