They sent me a not very interesting but quite complicated assignment on the CodeSignal. The platform worked bad, lost my a lot of my changes at one moment, and almost never compiled, but not because of my code. So I spent some time setting up environment locally, where everything compiled and I could run open tests. In the end I finished after the deadline, but sent the code in the email, describing the situation. I didn't receive any reply directly to my email, but received a rejection. I asked about my email, and turned out that they did consider my new code, but it didn't pass all the hidden tests (that I couldn't run myself, because the platform didn't work properly). So, about 6 hours lost writing a code, not to get even an interview