SSL error when retrieving the wsdl when creating labels from Shipment

[Nielex]

Since today we get an error on retrieving of the WSDL for Shipments (https://public-dis.dpd.nl/Services/LoginService.svc?singleWsdl):

ErrorException: Warning: file_get_contents(): SSL operation failed with code 1. OpenSSL Error messages:
error:1416F086:SSL routines:tls_process_server_certificate:certificate verify failed
#28 ./app/code/DPDBenelux/Shipping/Helper/DPDClient.php(188): DPDBenelux\Shipping\Helper\DPDClient::getSoapClient
#27 ./app/code/DPDBenelux/Shipping/Helper/DPDClient.php(59): DPDBenelux\Shipping\Helper\DPDClient::login
#26 ./app/code/DPDBenelux/Shipping/Helper/Services/AuthenticationService.php(92): DPDBenelux\Shipping\Helper\Services\AuthenticationService::getAccessToken
#25 ./app/code/DPDBenelux/Shipping/Helper/Services/DPDPredictService.php(217): DPDBenelux\Shipping\Helper\Services\DPDPredictService::generateLabel
#24 ./app/code/DPDBenelux/Shipping/Helper/Data.php(156): DPDBenelux\Shipping\Helper\Data::createShipment
#23 /./app/code/DPDBenelux/Shipping/Controller/Adminhtml/Shipping/PrintLabels.php(131): DPDBenelux\Shipping\Controller\Adminhtml\Shipping\PrintLabels::execute
#22 ./vendor/magento/framework/App/Action/Action.php(108): Magento\Framework\App\Action\Action::dispatch
#21 ./vendor/magento/module-backend/App/AbstractAction.php(231): Magento\Backend\App\AbstractAction::dispatch
#20 ./vendor/magento/framework/Interception/Interceptor.php(58): DPDBenelux\Shipping\Controller\Adminhtml\Shipping\PrintLabels\Interceptor::___callParent
#19 ./vendor/magento/framework/Interception/Interceptor.php(138): DPDBenelux\Shipping\Controller\Adminhtml\Shipping\PrintLabels\Interceptor::Magento\Framework\Interception\{closure}
#18 ./vendor/magento/module-backend/App/Action/Plugin/Authentication.php(143): Magento\Backend\App\Action\Plugin\Authentication::aroundDispatch
#17 ./vendor/magento/framework/Interception/Interceptor.php(135): DPDBenelux\Shipping\Controller\Adminhtml\Shipping\PrintLabels\Interceptor::Magento\Framework\Interception\{closure}
#16 /vendor/magento/framework/Interception/Interceptor.php(153): DPDBenelux\Shipping\Controller\Adminhtml\Shipping\PrintLabels\Interceptor::___callPlugins
#15 /DPDBenelux/Shipping/Controller/Adminhtml/Shipping/PrintLabels/Interceptor.php(26): DPDBenelux\Shipping\Controller\Adminhtml\Shipping\PrintLabels\Interceptor::dispatch
#14./vendor/magento/framework/App/FrontController.php(162): Magento\Framework\App\FrontController::processRequest
#13 ./vendor/magento/framework/App/FrontController.php(98): Magento\Framework\App\FrontController::dispatch
#12 ./vendor/magento/framework/Interception/Interceptor.php(58): Magento\Framework\App\FrontController\Interceptor::___callParent
#11 ./vendor/magento/framework/Interception/Interceptor.php(138): Magento\Framework\App\FrontController\Interceptor::Magento\Framework\Interception\{closure}
#10 ./vendor/magento/framework/Interception/Interceptor.php(153): Magento\Framework\App\FrontController\Interceptor::___callPlugins
#9 /Magento/Framework/App/FrontController/Interceptor.php(26): Magento\Framework\App\FrontController\Interceptor::dispatch
#8 ./vendor/magento/framework/App/Http.php(116): Magento\Framework\App\Http::launch
#7 ./vendor/magento/framework/Interception/Interceptor.php(58): Magento\Framework\App\Http\Interceptor::___callParent
#6 ./vendor/magento/framework/Interception/Interceptor.php(138): Magento\Framework\App\Http\Interceptor::Magento\Framework\Interception\{closure}
#5 ./vendor/justbetter/magento2-sentry/Plugin/GlobalExceptionCatcher.php(58): JustBetter\Sentry\Plugin\GlobalExceptionCatcher::aroundLaunch
#4 ./vendor/magento/framework/Interception/Interceptor.php(135): Magento\Framework\App\Http\Interceptor::Magento\Framework\Interception\{closure}
#3 ./vendor/magento/framework/Interception/Interceptor.php(153): Magento\Framework\App\Http\Interceptor::___callPlugins
#2 /Magento/Framework/App/Http/Interceptor.php(26): Magento\Framework\App\Http\Interceptor::launch
#1 ./vendor/magento/framework/App/Bootstrap.php(261): Magento\Framework\App\Bootstrap::run
#0 /index.php(41): null

At this point we can't print any labels. We use the latest version of you module 1.2.0.

Let me know if you need more information.