IXL Learning Senior UI Designer interview questions

The interview process was smooth in the beginning. I had a call with one of the designer asking about my experience and give a bit of background on the role. The part of the process that went sour was the design challenge. The assignment was to help improve the UI on one of the product screen. I did the assignment, handed it in and the next thing I received was an auto rejection email. Advice to the hiring manager, the design challenge should be fair to the candidate. The questions should not be part of the existing product and generate a scenario that both the candidate and the interviewer can discuss about. Design is a process, not just about getting the answer.