Can't connect to SAP Server with MQTT over WSS

I try since 3 Days to connect to the SAP MQTT over WSS (wss://iotmmsXXXXXXXXX.hana.ondemand.com/com.sap.iotservices.mms/v1/api/ws/mqtt).

With this I'm using a p12 client certificate.

But it goes to stuck on/ after the Handshake (see Wireshark Picture).

10.XX.XX.XXX is my IP

155.XX.XX.XXX is the SAP IP

After 30 seconds i got this error: And he try to connect again.

Here is the Source:

const fs = require('fs');
const mqtt = require('mqtt');

// Parts of URL and Path
const hcp_account_id = 'WWWWWWWWW';
const hcp_landscape_host = '.hana.ondemand.com' // this is used on PROD with Client Certificate Authentication
const my_endpoint_url_path = '/com.sap.iotservices.mms/v1/api/ws/mqtt';

//Certificate
const client_p12 = "./YYYYYYYY-YYYY-YYYY-YYYY-YYYYYYYYYYYY.p12";

// the following values need to be taken from the IoT Cockpit
const device_id = 'XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX';
const message_type_id_From_device = 'ZZZZZZZZZZZZZZZZZZZZ';

// for down- upstream communication
var my_publish_topic = "iot/data/" + device_id;
var my_subscription_topic = "iot/push/" + device_id;

var my_endpoint = "iotmms" + hcp_account_id + hcp_landscape_host;

var wsoptions =
    {
        host: my_endpoint,
        port: 443,
        pfx: fs.readFileSync(client_p12),
        passphrase: 'AAAAA',
        checkServerIdentity: false,
        protocol: 'mqttv3.1',
        protocolVersion: 13,
        perMessageDeflate: true,
        client_max_window_bits: true
    }

var options =
    {
        wsOptions: wsoptions,
        clientId: device_id,
        protocolId: 'MQIsdp',
        protocolVersion: 3,
        protocol: 'wss',
        hostname: my_endpoint,
        port: 443,
        path: my_endpoint_url_path
    }

const mqttc = mqtt.connect(options);

mqttc.subscribe(my_subscription_topic, 0);

mqttc.on('connect', () => console.log('connected!'));

mqttc.on('error', (msg) => console.log('error: ' + msg));

mqttc.on('offline', (msg) => console.log('offline: ' + msg));

mqttc.on('close', (msg) => console.log('close: ' + msg));

// message is Buffer
mqttc.on('message', (topic, message) => console.log('message(' + topic + '): ' + message.toString()));

I have resolved it with chaning the "sendPacket" method in "mqtt/lib/client.js" to

function sendPacket (client, packet, cb) {
  client.emit('packetsend', packet)
  var result = false
  try {
    var buf = mqttPacket.generate(packet)
    result = client.stream.write(buf)
  } catch (err){
    client.emit('error', err)
    result = false
  }
  if (!result && cb) {
    client.stream.once('drain', cb)
  } else if (cb) {
    cb()
  }
}