I've tried that approach in a couple of interviews and, no surprise, I did not get those jobs because interviewers really seem to hate it if you dare step outside the little cocoon of leet they've constructed.

It doesn't matter why you can't fix the server, you can't fix the server. It doesn't matter why it can only handle one request at a time, it can only handle one request at a time. That information doesn't change the solution to the task. Make up whatever you please - maybe it's a third party system so you can't access the code. Now try to come up with some useful questions that actually help you solve the task instead of wasting time asking pointless questions.

No wonder people reject you if this is how you approach interviews. Maybe it would make sense to ask these kinds of questions in a real work scenario, but it does not make sense in an interview where you are given a made up task. Just accept the constraints and solve the problem. You sound like a high school student being intentionally obtuse, like you came into the interview thinking you're too good to be evaluated that way or maybe you just don't have a clue how to solve the actual problem you're given so you try to stall to avoid having to admit that you can't do it.