QBO API v3 PHP call returns NULL - php

Question

I'm using the qbo-api-v3 for PHP to authenticate and retrieve a Balance Sheet report via PHP script. This has been working just fine over the last 6 months, but recently stopped returning data (returns NULL for repsonseCOde, responseBody, and responsArray). I can't figure out why - any ideas? Thanks!
// qbo API
require_once dirname(__FILE__).'/../v3-php-sdk-2.2.0-RC/config.php';
require_once(PATH_SDK_ROOT . 'Core/ServiceContext.php');
require_once(PATH_SDK_ROOT . 'PlatformService/PlatformService.php');
require_once(PATH_SDK_ROOT . 'Utility/Configuration/ConfigurationManager.php');
require_once(PATH_SDK_ROOT . 'Core/CoreHelper.php');
require_once(PATH_SDK_ROOT . 'DataService/Batch.php');
require_once(PATH_SDK_ROOT . 'DataService/IntuitCDCResponse.php');
require_once(PATH_SDK_ROOT . 'Data/IntuitRestServiceDef/IPPAttachableResponse.php');
require_once(PATH_SDK_ROOT . 'Data/IntuitRestServiceDef/IPPFault.php');
require_once(PATH_SDK_ROOT . 'Data/IntuitRestServiceDef/IPPError.php');
require_once('RestServiceHandler.php');
require_once(PATH_SDK_ROOT . 'Core/OperationControlList.php');
// QBO Service Context
$serviceType = IntuitServicesType::QBO;
$oauth['AccessToken'] = ...
$oauth['AccessTokenSecret'] = ...
$oauth['ConsumerKey'] = ...
$oauth['ConsumerSecret'] = ...
$oauth['RealmID'] = ...
$requestValidator = new OAuthRequestValidator(ConfigurationManager::AppSettings('AccessToken'),
ConfigurationManager::AppSettings('AccessTokenSecret'),
ConfigurationManager::AppSettings('ConsumerKey'),
ConfigurationManager::AppSettings('ConsumerSecret'));
$serviceContext = new ServiceContext($oauth['RealmID'], $serviceType, $requestValidator); //d($serviceContext);
if (!$serviceContext) exit("Problem while initializing ServiceContext.\n");
// query for Balance Sheet Report - https://developer.intuit.com/docs/api/accounting/balance%20sheet
$report = 'BalanceSheet';
$query = "start_date=$start_date&end_date=$end_date";
$uri = "company/{1}/reports/$report?{2}";
$uri = str_replace("{1}", $oauth['RealmID'] , $uri);
$uri = str_replace("{2}", $query , $uri);
// Creates request parameters
$requestParameters = new RequestParameters($uri,'GET',CoreConstants::CONTENTTYPE_APPLICATIONJSON, NULL);
$restRequestHandler = new RestServiceHandler($serviceContext);
// Make the request
list($responseCode,$responseBody) = $restRequestHandler->GetReportsResponse($requestParameters, NULL, NULL);
$responseArray = json_decode($responseBody, true);