Interview Questions › Root Cause Analysis

A key product metric (DAU) suddenly drops by 5%

You are a PM on a flagship consumer social app. Your primary health metric, Daily Active Users (DAU), suddenly dropped by 5% yesterday. Investigate the cause.

Context

The alert triggered during the daily morning executive sync. Weekly active users (WAU) are relatively stable over the 7-day trailing window.

Clarifying questions to ask first

• Is this drop global or localized?
• Did sessions/events also drop or just unique user IDs?
• Was there a deployment in the last 24-48 hours?

How to approach it

1. Clarify metric definition (what counts as an active user: session open vs passive background sync)
2. Segment by Platform (iOS, Android, Web), Geography, App Version, and Network Carrier
3. Check internal releases, auth outages, logging/telemetry bugs, and app store updates
4. Examine external factors: holidays, regional internet outages, competitor events
5. Propose immediate triage and telemetry validation steps

Framework: Clarify Metric & Bounds -> Segment by Dimensions -> Internal (Release/Telemetry/Infra) vs External -> Root Cause Confirmation -> Action Plan

Sample answer

• Telemetry logging pipeline latency
• Auth token expiry bug in latest app build
• Android OS version update causing crash on launch

1. Check logging dashboard health
2. Segment by OS version -> isolate Android v14.2 spike in crash rate
3. Identify bad null-pointer in feed initialization

Executive summary: 5% DAU dip isolated to Android v14.2 release crash loop affecting 1.2M users; rolled back release and deployed hotfix within 2 hours.

What interviewers look for

• DAU / WAU Ratio
• Crash Rate
• Login Success Rate
• Telemetry Pipeline Health
• Session Duration