Your question is Diagnose Engagement 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 you noticed a sudden drop in our primary engagement metric, how would you go about diagnosing the root cause?
Assume the metric and affected population are not yet defined. Explain how you would validate the signal, narrow the affected users and product surfaces, investigate likely causes, and determine whether the decline reflects a measurement issue or a real change in user behavior. Prioritize your investigation and describe what evidence would support each hypothesis.