StackHawk Senior Front End Engineer interview questions

I was contacted through a 3rd party recruiter. They gave me an overview and setup a call with the company's CSO. The CSO cancelled a few hours before the first interview, which was inconvenient for me as it's not easy to get out of the office for these calls. The CSO didn't reach out to me, but I was told through the recruiters assistant. I didn't hear anything for a few days, but they later rescheduled for a 2nd try. I talked to the CSO for 30 minutes. We ran through pretty standard questions, and I asked some of him as well. It was overall a positive experience. The next step was to complete an exercise. The ask was to fork their repo and implement the front end of a simple CRUD app. I completed this exercise about 2 or 3 days after we spoke and submitted it to the CSO. I enjoyed the exercise and felt it was an appropriate request. I never recieved a reply that my submission was recieved. There was no response until I was rejected, 9 days later. There wasn't much feedback provided, though I didn't expect much as I know it puts companies in a difficult situation. I think the communication could have been improved. I understand that they're a startup and everyone is busy, but just a few words in a quick email sends a much different signal.