Hi Jerry,
Have you changed the attribute name, i did not see the STRUCT.PRODUCT_ID in above screen shot. keep break point in GET_S_STRUCT method in context node class and see whether the structure is having product id or not. All attributes in context node get method will be triggered from GET_S_STRUCT method.
Check you are using STRUCT.PRODUCT_ID field in web ui configuration.
Best Regards,
Dharmakasi.