We have a live React app connected to a Python FastAPI backend. Complex JSON responses from a Python model are not rendering correctly in the app. Arrays return properly, but nested fields arrive as null or malformed once received in React. We need a developer experienced with both FastAPI (Pydantic models/serialization) and React(state management and API parsing using fetch/axios). The task is to identify where the nested data is breaking, correct the serialization/decoding, and ensure the full object structure renders properly in the UI. No new features are required. This is a focused debugging task intended for someone who can quickly trace, diagnose, and resolve data structure issues across both frontend and backend.