I had 2 different interviews in a year range with different recruiters. Unfortunately they both didn't have much information about the client project.
First time I passed HR interview and got it to the client but I was completely unaware that it would be a system design interview, because I was told that it would be 'nothing serious', just an easy tech scan and I can ask my questions about the project, as there was supposed to be a client's HR (there wasn't). That's probably ok in general but in my case it was brutal as it was my first system design interview ever as I'm from another country where it's not common, I got super nervous. So, no surprise, I failed. Probably I would've failed even if I knew about the system design :) I guess that it could be a communication problem on the client side, I informed recruiter about it. I also was told that the team was all juniors and they need a mentor, but in reality it was all seniors and the guy on the client side was surprised (and actually pretty annoyed with me asking all the questions I was told I could ask).
My second time was as well with someone not aware of client projects which is probably usual for agencies but I personally don't like spending my time on something completely unknown, not even field. Recruiter read some client's questions from screen and there was also an AI on call to write all the call so they could pass it to the client (at first time there was AI as well).
