Slack Developer interview questions

Got an email saying thanks for finishing the coding challenge but I was not being moved forward, when I didnt even take the coding challenge. I emailed, got a phone call that they are interested the next day, had a short talk, the person I spoke to said will get back to me if the devs want to proceed after viewing my resume. The next day got an email saying they will not move on. Dont waste your time here. I am sure the hr person messed up, but didnt want to get any backlash, so just made a call and refused me right after.

After a quick phone call with the recruiter, they presented me with a coding exercise. It is a project that you have to finish in one week. My project was a binary memcache protocol implementation (get and set commands only). The protocol is supported by famous memcached. I submitted my implementation on time, and after another week I got a call from the recruiter who informed me that my implementation doesn't meet some never unspecified criteria. I have never been contacted by a Slack engineer. After spending a week, I would expect some technical feedback, discussion, comments, questions. I find that kind of response somewhat unprofessional and disrespectful. If you'd rather not wasting a week, or the exercise isn't something that is very interesting for you, I would not bother with Slack.