When a funnel step collapses overnight, product instinct says redesign. Instrumentation instinct asks what shipped in the release that touched that screen.
We compare event volume against app version, locale, and acquisition channel before calling churn. In several Gwanak-based products, the “crisis” was a renamed screen that stopped firing the activation event.
Lock the definition of the step, then check whether the definition still matches the UI. If the event fires on a different surface after a redesign, your historical route is broken even if users are fine.
Keep a one-page release checklist for analytics owners: new screens, renamed CTAs, and any identity change. Ten minutes of checklist beats two weeks of panic analysis.