I didn't realize I wouldn't be able to edit the "test script" section. Here's the PR with a test: https://github.com/php/php-src/pull/2153

I have a problem that can be similar.
PHP version 5.6 SOAP communication was occurring correctly, but when upgrading to version 7.0.11, the operation became incorrect.
Below the section of code that runs on PHP 5 but does not work in php 7.

protected function zSendSOAP($urlService, $dataArray, $operaration) {
   ini_set("soap.wsdl_cache_enabled", "0");

   $options = array(
       'location' => $urlService,
       'uri' => 'http://schemas.xmlsoap.org/soap/envelope/',
       'local_cert' => $this->certKEY,
       'soap_version' => SOAP_1_2,
       'cache_wsdl' => WSDL_CACHE_NONE,
       'connection_timeout' => 15,
       'encoding' => 'UTF-8',
       'trace' => 1,
       'exceptions' => 1
    );

    $urlWsdl = $urlService . '?wsdl';
        
    $soap = new SoapClient($urlWsdl, $options);

    $obterOperacaoTransportePdf = array(
        'ObterOperacaoTransportePdfRequest' => array(
          'Integrador' => '761ba43d-dc74-4900-85bf-70853fcae4a9',
          'Versao' => '1', 
          'CodigoIdentificacaoOperacao' => '161000003705/1660',
          'DocumentoViagem' => ''
        )
    );

    $data = $soap->$operaration($obterOperacaoTransportePdf);
        
    return $data;
}

On the server that receives the data, the key "Integrator" is not being received, and possibly other data is also not being received.

The strange thing is that this code works seamlessly with PHP 5.6.