MQTT broker issue

I started using the MQTT Server and Webclient addon (HA is running on HassOS) but i am running into some issues as HA is not able to connect to the MQTT server and no mqtt sensor are showing up anymore while the nodered addon can connect, receive and send messages without any problems.

Here is the error shown in the log:

2018-10-22 15:31:56 ERROR (MainThread) [homeassistant.core] Error doing job: Task exception was never retrieved
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/homeassistant/helpers/entity_platform.py", line 352, in _async_add_entity
    await entity.async_added_to_hass()
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/sensor/mqtt.py", line 173, in async_added_to_hass
    message_received, self._qos)
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/mqtt/__init__.py", line 280, in async_subscribe
    topic, msg_callback, qos, encoding)
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/mqtt/__init__.py", line 662, in async_subscribe
    await self._async_perform_subscription(topic, qos)
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/mqtt/__init__.py", line 697, in _async_perform_subscription
    _raise_on_error(result)
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/mqtt/__init__.py", line 782, in _raise_on_error
    'Error talking to MQTT: {}'.format(mqtt.error_string(result_code)))
homeassistant.exceptions.HomeAssistantError: Error talking to MQTT: The client is not currently connected.

I guess this message is appearing as HA tries to connect to the MQTT broker while its not yet started but i am not sure.

My config is as follows:

mqtt:
  broker: hassio.local
  port: 4883
  client_id: ha_mqtt
  username: !secret mqtt_broker_username2
  password: !secret mqtt_broker_password2
  certificate: /ssl/certificate.pem

A sensor for example:

  - platform: mqtt
    name: floortemp
    unit_of_measurement: '°C'
    state_topic: "home/floor/floortemp"

I have had another MQTT broker running on another server and the sensors were working fine…

Any ideas what this could be about ?

Is there a way to delay the startup of the HA mqtt connection to the broker in hassos? I think this might be the issue.