If you are running into an issue where your REST based SmartObjects are only returning the HTTP response code and no data, or the data is blank, there is a simple fix. This issue is related to having a strange character or . (Period) character in the Service Instance System Name. This causes the K2 REST Broker to be confused and have a tough time returning values, only returning empty values and the HTTP Response code.
Resolution:
Simply recreate the REST Service Broker not using a strange character. Also recreate your smartobjects and you should see the SmartObjects returning all the correct data.