Do not update platform during startup

sensor.py

@@ -86,7 +86,7 @@ class AlertaSensor(Entity):
 
     async def async_update(self):
         """Get the latest data from Alerta API."""
-        await self.alerta.async_update()
+        self.alerta.async_update()
         self._state = 'ok'
         for alert in self.alerta.alerts:
             if alert.severity in ['security', 'critical', 'major']: