Revolut Sr Software Engineer interview questions

Applied to an offer in LinkedIn. Contacted by them, and scheduled the first interview. The first interview was just a 10 minutes talk with one interviewer. 5 minutes where she told me about Revolut and how they work, 3 minutes talking about my experience, and the rest for 2 plain questions about if I knew the complecity of a hashmap, and the meaning of transactionality. The questions were plainly read by her and there was no discussion at all, quite cold and. Rejected after it because of another more fitting candidate.

The first part of the interview was a quick screening with a recruiter asking some simple technical questions. The second part was a live coding exercise with a software engineer where I was required to write a LoadBalancer. I did write the balancer (very well in my opinion) however I had a flaw in my code which was not thread safe. I found the flaw and fixed it, however the interviewer seemed quite disappointed that I made the mistake in the first place. I can't really tell as he was very quiet during the whole interview and gave 0 feedback and even seemed annoyed when I asked him a question. I received a rejection afterwards, again with no feedback. So my advice is to focus a lot on multithreading as it seems that a simple mistake there is a dealbreaker.