Why Batch Request does not stick to json format provided?

I am trying to get the Gemini batch process output in a structured json I specified in the system instructions. I tried thrice: twice with 500 requests per batch and once with 186 using gemini 2.5 pro But every time the output does not follow the json structure. Although the json structure is a bit complex but 2.5 pro was able to give the output I want when I used it in real time.
Am I doing it wrong? Is there a better way to specify the json in batch processing?