It’s possible that your JSON response is not valid JSON. Technically, 001 is not a valid number type in JSON, but your cohortid uses 001. A valid number would be 1. If cohortid needs the leading 0’s, then it would be more appropriate for it to be a string type, like “001”.
I’m not sure if the CCG logs are capturing this type of error, but it can certainly cause issues with any tool that needs to consume JSON. You can see this error in action by pasting your sample in a JSON validator tool, like json validator at DuckDuckGo.
My educated guess is that cohortid is causing validation issues and preventing any JSONpath from working. If you have control over target webservice, then making cohortid a string might fix this. If you don’t have control, then I suspect you will need to create an after operation rule to manually parse this response.