I, too, had a very negative and time-wasting experience in the technical "brainteaser" round at Cruise. As of today, a whopping 45% of candidates reported a negative experience whilst interviewing at this company, and now it's obvious why.
For the technical round for software engineers, even very senior engineers like me, they're still hell-bent on using the archaic system of calling someone over a cell phone and putting the candidate through a coding challenge. This method may work for junior engineers with no experience to verify, but it's a shameful disgrace that they use this to supposedly find very senior level engineers with vast knowledge in our field. I expected more from Cruise's management, especially being a GM company, infused with billions in cash.
My interviewer started outside on a noisy street with sirens (typical SF), very hard to hear what he was saying, and he was muffled. When he finally got indoors, his voice was still muffled and about 10 minutes in, the call dropped. My S8+/Verizon has never arbitrarily dropped at call like this, and I am quite confident that it was on his end. Anyway, I lost 5 minutes there, but we reconnected. His voice was still muffled, but I was able to make out most of what he was saying.
Then we got to the college-level brainteaser. He didn't explain what he wanted particularly well, and when I asked to clarify, it helped but still didn't fully describe the problem. This could have been in part to the muffled connection. But I was able to talk successfully through my plan to solve it, but I wasn't able to finish my code to a runnable state, forgetting one particular syntax in Python which any engineer can do from time to time.
Because a random interviewer's cell phone was muffled, and because I didn't complete the cute little brainteaser, they blundered and missed a major opportunity here, and I would presume this is why the company's growth is so chaotic and patchy with a lot of bad hiring decisions & turnover. Although you can't necessarily confirm this with just the reviews/reports on this website, there is a very obvious trend if you read through them.
I'm inclined to say that this process is downright ageist, meant to naturally weed out older engineers like myself who haven't had to deal with these useless code brainteasers with a 30-minute limit in over 12+ years. This company cannot continue on this course with a trashy, unbaked interview process such as this.