Miele gateway discovered but communication seems broken


we recently bought a Miele@home enabled washing machine which includes the Zigbee-Gateway. I’m seeing the machine in the Miele@mobile app and OpenHAB2 can discover the gateway correctly. However, after that, it seems not to be able to communicate with the gateway for dicsovery of attached things:

2017-02-22 19:09:17.593 [INFO ] [g.discovery.internal.PersistentInbox] - Added new thing 'miele:xgw3000:Miele_WMG823' to inbox.
2017-02-22 19:09:29.347 [DEBUG] [org.openhab.binding.miele           ] - ServiceEvent REGISTERED - {org.eclipse.smarthome.config.discovery.DiscoveryService}={service.id=357, service.bundleid=219, service.scope=singleton} - org.openhab.binding.miele
2017-02-22 19:09:29.375 [DEBUG] [ing.miele.handler.MieleBridgeHandler] - Initializing the Miele bridge handler.
2017-02-22 19:09:29.377 [DEBUG] [ing.miele.handler.MieleBridgeHandler] - Scheduling the Miele polling job
2017-02-22 19:09:29.379 [DEBUG] [ing.miele.handler.MieleBridgeHandler] - Scheduling the Miele event listener job
2017-02-22 19:09:29.397 [ERROR] [ing.miele.handler.MieleBridgeHandler] - An unexpected status code was returned : '404'
2017-02-22 19:09:29.399 [ERROR] [ing.miele.handler.MieleBridgeHandler] - An exception occurred while posting data : ''
2017-02-22 19:09:29.400 [DEBUG] [ing.miele.handler.MieleBridgeHandler] - is not reachable

I can ping the gateway but calling the URL from the browser always gives a 404.

Can anyone give me a hint on what is wrong there?

Thanks in advance,