Why does React DevTools’ “Why did this render?” sometimes miss certain re renders or stale closures in function components?

Explains limitations of new profiling plugins in detecting memoization and hooks closure updates.

React DevTools 5.0 (released mid 2025) added a “Why did this render?” panel and a “Memory profiler” / “leak detection” plugin to help identify unnecessary re renders and retain objects past unmounts . However, it has two main blind spots:

1. Stale closures in function components It compares hook closure references (e.g. an onClick callback passed to a child) rather than actual values captured. If you update shared state via context or refs but the callback identity doesn’t change, the profiler won’t flag the render—even though the logic inside might behave incorrectly.
2. Memoization edge cases and batching The profiler doesn’t always alert when React renders due to context changes or batched updates. If a component is wrapped in React.memo but its parent forces an update, or if multiple events batch together, the tool may misattribute the render to the parent or context rather than the memo boundary. ➡️ Tip: Always verify by profiling with visual change in the component or checking behavior with strict mode. If in doubt, rely on custom debugging (e.g. useWhyDidYouUpdate) until profiler coverage expands.