You are the PM of Messenger and notice a significant drop in DAU. How would you investigate the cause?

To investigate a drop in Messenger's Daily Active Users (DAU), I would first clarify the definition of 'active' (e.g., sending/reading messages, opening the app) and the timeframe of the decline. Assuming the drop occurred over the last 30 days, I'd then analyze the data to identify specific user segments, features, or regions most affected. I would also check for external factors like seasonality (e.g., holidays, school schedules), competitor activity, or technical issues (e.g., app performance, bugs, network problems). Simultaneously, I'd review recent product changes, marketing campaigns, and user feedback to pinpoint potential causes. If the cause remains unclear, I'd formulate hypotheses and design A/B tests or user research to validate them.