DEBUG: Cache is NOT active
DEBUG: try to retieve this url: https://www.wazzuprealestate.nl/api/statistics/
DEBUG: wp_remote_get to https://www.wazzuprealestate.nl/api/statistics/
DEBUG: arguments: Array ( [timeout] => 500 )
DEBUG: error getting URL: cURL error 28: Resolving timed out after 10520 milliseconds
DEBUG: no data received: check url of json-feed

EMPTY api-answer: No JSON received - is the API down? Check the URL you use in the shortcode!