I also faced the same problem. Hurricane labs app is querying Shodan and providing the results. I figured out in my case, the API is broken. Shodan REST API documentation (link below) specifies that net filter to be used for the CIDR notation. However, I know the API key works as I tested with the 126.96.36.199, but it wont work for CIDR, for ex: query=net:188.8.131.52/30 (which ideally should return the results)
You can try this on your browser with your API key and query as per the document.
I presume if this gets fixed then the app will work for CIDR.