Your question is Diagnosing a 10% Metric Drop. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
If our core engagement metric drops by 10% overnight, what is your systematic process for diagnosing the root cause?
Treat the metric definition and product context as unspecified. Explain how you would distinguish a measurement or data-quality issue from a genuine user-behavior change, decompose the movement, prioritize hypotheses, and communicate findings.