Update react-router.mdx

docs/platforms/javascript/guides/react/features/react-router.mdx

@@ -84,7 +84,7 @@ You can instrument [`createMemoryRouter`](https://reactrouter.com/en/main/router
 
 ### Custom Error Boundaries
 
-When using `react-router`, errors thrown inside route elements will only be re-thrown in **development mode**. In production, these errors won't be surfaced unless manually captured. If you **don't** have a custom error boundary in place, `react-router` will create a default one that "swallows" all errors.
+When using `react-router`, errors thrown inside route elements will only be re-thrown in **development mode** while using [`strict mode`](https://react.dev/reference/react/StrictMode). In production, these errors won't be surfaced unless manually captured. If you **don't** have a custom error boundary in place, `react-router` will create a default one that "swallows" all errors.
 
 <Note>
 Note, that this only applies to render method and lifecycle errors since React doesn't need error boundaries to handle errors in event handlers.
@@ -119,7 +119,9 @@ import * as Sentry from "@sentry/react";
 export function YourCustomRootErrorBoundary() {
   const error = useRouteError() as Error;
 
-  Sentry.captureException(error);
+  React.useEffect(() => {
+    Sentry.captureException(error);
+  }, [error]);
 
   return (
     <div>