Spotify Component disappearing

I am running the latest Home Assistant via Docker on my Raspberry Pi 3
After setting up the Spotify Component as described in the guide, with my local IP as my base_url and the correct URL on the Spotify developer page, I can get HA to authenticate.
Namely, it connects to my Spotify Account and appears in the List of my approved Applications. After that, the Spotify Widget just disappears, leaving me with a blank canvas.
In my Log, there is an entry “Spotify changed to configured”
Looking closely, there is no Spotify Token Cache anywhere to be found, neither with a custom cache_url nor with the standard one.
My logfile has the following lines:

17-05-04 20:23:34 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/", line 361, in async_process_entity
        new_entity, self, update_before_add=update_before_add
      File "/usr/local/lib/python3.6/site-packages/homeassistant/helpers/", line 191, in async_add_entity
        yield from self.hass.loop.run_in_executor(None, entity.update)
      File "/usr/local/lib/python3.6/concurrent/futures/", line 55, in run
        result = self.fn(*self.args, **self.kwargs)
      File "/usr/local/lib/python3.6/site-packages/homeassistant/components/media_player/", line 158, in update
        devices = self._player.devices().get('devices')
    AttributeError: 'NoneType' object has no attribute 'get'

May anybody provide any assistance at all?
Thanks in Advance!