All questions like this are really saying “tell me about yourself as an engineer. Here’s a prompt.”

“What’s the most elusive bug you’ve ever fixed?” is a worse question, because it tells me less about you as an engineer, and more about the specific problems you’ve worked on. It’s a worse question to get to the heart of who you are - which is the whole point.

And, because the point is to get to know the person, you have way more breadth in your answer than you think. “Well, I don’t have a favorite bug. I hate all bugs. But I do remember a bug so horrible it took down our site at least once a day for a month…”. This is a fantastic answer - since it answers the real question underneath, of who you are.