Problem with subscription to MQTT Broker

[Thosch42]

Hi all!
I added a subscribtion to my MQTT Broker (Mosquitto on a RPi3) to receive some timing settings. Did it all straight forward like in the example, no fancy things.
Unfortunately, the callback function is only triggered once, right after subscribe. Here's a little snippet:

def cb_Get_Settings(topic, msg):
    print("+++++++++++++++++++++++++++++++++\n" * 2)
    print(topic, ' : ', msg)
    print("+++++++++++++++++++++++++++++++++\n" * 2)

def start_wlan():
    global wlan
    global mqtt
    wlan = WLAN(mode=WLAN.STA, power_save=False)
    wlan.connect(config.WIFI_SSID, auth=(WLAN.WPA2, config.WIFI_PASS), timeout=5000)
    print("Try to connect to Wifi...", end='')
    wifi_ok = False
    for _ in range (10):
        if wlan.isconnected():
            wifi_ok = True
            break
        else:
            time.sleep(1)

    if wifi_ok:
        #pycom.rgbled(0x550000)
        print("Done!!!")
        wifiaddress = "IP Address is: " + ((str(wlan.ifconfig()[:1]))[2:])[:-3]
        print(wifiaddress)
        print("Connect to MQTT Broker at " + config.MQTT_BROKER + "...", end='')
        mqtt = MQTTClient(config.UNIQUE_ID, config.MQTT_BROKER, keepalive=1, port=config.MQTT_PORT)
        mqtt.settimeout = settimeout
        mqtt.set_last_will(config.LAST_WILL_TOPIC,  config.LAST_WILL_MSG,  retain = True,  qos = 1)
        mqtt.set_callback(cb_Get_Settings)
        mqtt.connect(clean_session=False)
        mqtt.publish(config.LAST_WILL_TOPIC, config.LAST_WILL_BACK, retain=True, qos=1)
        print("Done!!!")
        print("Subscribe to Settings Topic...")
        subTopic = config.MQTT_DEVICE_NAME +"/settings/get"
        mqtt.subscribe(topic=subTopic, qos=1)
        print("Done!!!")
    else:
        maschine.reset()

When ever I send I message to the topic I subscribed to, I get nothing.
I tried to use mqtt.check_msg() on top my main loop. Then I receive the messages, but check_msg blocks the main loop, so everything inside the main loop is only executed if I publish a message to the subscribed topic.
What I now wondering is something in the official Pycom MQTT library.
Snipp---------

# Checks whether a pending message from server is available.
# If not, returns immediately with None. Otherwise, does
# the same processing as wait_msg.
def check_msg(self):
    self.sock.setblocking(False)
    return self.wait_msg()

Is there really any check done? For me, it just runs wait_msg(), isn't it?

Cheers,
Thomas

[Thosch42]

Ok, some news:
If I publish something to any of my topics with QoS set to 1, I can receive the message from the topic I subsrcibed to, but, unfortunately, only one time. The callback function runs fine, but then, the main loop is blocked.
I can see, that the sensor threads are still running fine, but there are no more data published, because of the blocked main loop.

Cheers,
Thomas