The interview process was pretty standard. I had two in-person meetings in London. One was to present a task, which was very detailed and time consuming to prepare - it was more like 3 tasks in 1. Like others have said, there was a focus on working long hours/overtime, which was a red flag.
The negative experience came after the interview. First, the hiring manager emailed me mistaking me for another candidate. When I replied, she had a feeble explanation. Then when I asked for news about the role I applied for, she ghosted me. I sent two chasers and got nothing back. I think that is really bad manners considering the amount of time I spent on the task and the fact that I was good natured about her email mixup. Overall my impression is that they lack professionalism or are so overworked that they get sloppy.