Microsoft Senior Software Developer Engineer interview questions

The interview process was standard. This requirement was for Azure team The first round consisted of a medium-level LC coding problem and some OS related questions. I was able to solve the problem and run through test cases but took few mins to debug for a particular test case. So the feedback was borderline. The second round had some project-related questions, scenario-based questions, and one medium LC problem. The feedback was good. The third round consisted of a system design problem. Although, I covered the all the points but the interviewer was expecting some more details especially around the services. The feedback was borderline. - The second and third round feedback seemed fair. I still didn't understand why the first round feedback was borderline.