MQTT_ERR_NOMEM should not result in a reconnection

CHANGELOG.md

@@ -11,6 +11,8 @@ Given the high speed of development in the first phase, changes are being report
 
 - Fixed dashboard widgets custom classes being propagated both to the container and to the widget content [see #179]
 
+- Added reconnection logic to `backend.mqtt` listeners in case of temporary MQTT server-side errors.
+
 ## [0.20.6] - 2021-03-16
 
 ### Added

platypush/backend/mqtt.py

@@ -83,7 +83,7 @@ class MqttClient(mqtt.Client, threading.Thread):
         # noinspection PyUnusedLocal
         def handler(client, userdata, rc):
             if not self._stop_scheduled and rc in {mqtt.MQTT_ERR_INVAL, mqtt.MQTT_ERR_AGAIN, mqtt.MQTT_ERR_CONN_LOST,
-                                                   mqtt.MQTT_ERR_CONN_REFUSED, mqtt.MQTT_ERR_NOMEM, mqtt.MQTT_ERR_ERRNO,
+                                                   mqtt.MQTT_ERR_CONN_REFUSED, mqtt.MQTT_ERR_ERRNO,
                                                    mqtt.MQTT_ERR_NO_CONN, mqtt.MQTT_ERR_PAYLOAD_SIZE,
                                                    mqtt.MQTT_ERR_QUEUE_SIZE, mqtt.MQTT_ERR_UNKNOWN}:
                 self.logger.warning('Unexpected disconnection from {}:{}. MQTT error: {}'.format(