Developers using HarmonyOS with the @Observed decorator often find UI reactivity breaks when assigning plain JSON data from a server. The core issue is that fetched JSON objects lack the necessary class metadata for the framework's change detection system to track property modifications.

To restore functionality, the data must be converted into proper class instances. The solution involves using the class-transformer library's plainToClass method alongside reflect-metadata. This process wraps the plain object, ensuring the decorated class properties are reactive and UI updates trigger correctly.

This pattern is critical for any app loading dynamic lists or objects from an API and binding them to UI components like @State or @ObjectLink. Without this type restoration step, developers will see static interfaces that don't reflect data changes, a common pitfall when working with external data sources in this framework.