deconz-rest-plugin: Internal error 951

Hi!

A user of home assistant and deconz gets this error: [pydeconz.utils] HTTP request response: [{'error': {'address': '/groups/5', 'description': 'Internal error, 951', 'type': 901}}] when sending [pydeconz.utils] Sending {'data': '{"on": false}'} to http://*IP*:*PORT*/api/*API_KEY*/groups/5/action

What does that error actually mean?

Original issue reported here: https://github.com/home-assistant/home-assistant/issues/22852