Assertion teststep fails with error "Failed- null/empty response body"

I am creating assertion teststep for JSONPath match for existing JSON content (read from file using Groovy) with the one from Response of the GET request. If checked in assertion UI with 'Test' functionality it shows 'Matches content' & even Response content is verified using "Select from Current". 

So it mean though the response is available assertion teststep shows empty response body which is causing the failure.

The same thing works if I put the assertion of GET Req. teststep but for certain mechanism I have to use via assertion test step.

Thanks.