How it happens
Almost always in a refactor. A coding agent (or a human) rewrites a function, and the analytics line inside does not survive the rewrite. The function still works; the call just is not there anymore.
What breaks downstream
The funnel that depended on the event goes quiet. The dashboard keeps drawing from historical data, then flatlines. Activation rates appear to crash overnight. The first signal is usually a PM asking why a number looks weird.