ESP8266 umqtt OSError -1

So, I have an ESP8266. On this board I'm running the newest Version of the MicroPython firmware (1Mib).

I have a Java Vaadin Web Application with 2 Buttons. One Button is for publishing, that the LED should turn off and one Button for turn the LED on.

The MicroPython program on the ESP is running good, till I publish from the Vaadin App. I get the OSError -1 with no other args.

Some informations:Broker: hivemq in dockerhub localhostProgram for flashing: Thonny

Here is my MicroPython code: (I deleted the ssid and password for data protection -> the client sucessfully connect with the wifi)

import machinefrom umqtt.simple import MQTTClientimport networkimport timessid = "ssid"password = "password"wlan = network.WLAN(network.STA_IF)wlan.active(True)wlan.connect(ssid, password)while not wlan.isconnected():    passprint("hallo")MQTT_TOPIC = "led/control"LEDstatus = "off"ClientID = "Alabama"LED_PIN = machine.Pin(2, machine.Pin.OUT)LED_PIN.value(1)def mqtt_callback(topic, msg):    if msg.decode() == "on":        LEDstatus = "on"        LED_PIN.value(0)    elif msg.decode() == "off":        LEDstatus = "off"        LED_PIN.value(1)client = MQTTClient(b"Alabama", b"192.168.2.125", 1883)client.set_callback(mqtt_callback)client.connect()client.subscribe(MQTT_TOPIC)while True:    try:        client.check_msg()        time.sleep(10)    except OSError as e:        print("Fehler beim Empfangen der Nachricht:")        print(e.args)        client.disconnect()        break

here is my subscribe publish method in Java Vaadin:

public void publishToDashboard(String topic, String message, String clientID)            throws ExecutionException, InterruptedException, JsonProcessingException {        ObjectMapper objectMapper = new ObjectMapper();        Map<String, String> payload = new HashMap<>();        payload.put("clientID", clientID);        payload.put("message", message);        String strPayload = objectMapper.writeValueAsString(payload);        Mqtt5Publish mqttMessage = Mqtt5Publish.builder()                .topic(topic)                .payload(strPayload.getBytes())                .contentType("json")                .qos(MqttQos.AT_LEAST_ONCE)                .build();        this.client.publish(mqttMessage).get();        System.out.println("published");    }

also for the Java MQTT Client i'm using this one from hivemq.

and here is the method, that I call when a Button get clicked:

private void publishLED(ClickEvent<Button> event, String msg, String clientID) {        CompletableFuture.runAsync(() -> {            try {                client.publishToDashboard("led/control", msg, clientID);            } catch (ExecutionException | InterruptedException | JsonProcessingException ex) {                throw new RuntimeException(ex);            }        });    }

It's my first project with ESP8266 and MQTT, and I literally searched 5h for this Exception but i did'nt find something.

If any informations missing please let me know.

Thank you for trying to help me. :)

Have a good one

Tried: Published message from Web App with buttonExpected: ESP8266 catch the message with subscribe and turn LED on or offWhat happened: OSError -1