Troubleshoot Tado Device Tracker Configuration

I’m trying to set add my Tado Thermostat to a new home assistant installation on a Raspberry Pi.

Configuration.yaml section looks like this:

device_tracker:
  - platform: tado
    username: xxx
    password: yyy

On startup, home assistant returns the following output:

17-02-18 12:53:13 homeassistant.loader: Unable to find component device_tracker.tado
17-02-18 12:53:13 homeassistant.bootstrap: Unable to find platform device_tracker.tado
17-02-18 12:53:14 homeassistant.core: Bus:Handling <Event call_service[L]: domain=persistent_notification, service=create, service_call_id=3052993040-1, service_data=title=Invalid config, message=The following components and platforms could not be set up:
* device_tracker.tado
Please check your config, notification_id=invalid_config>
17-02-18 12:53:14 homeassistant.core: Bus:Handling <Event state_changed[L]: old_state=None, entity_id=persistent_notification.invalid_config, new_state=<state persistent_notification.invalid_config=The following components and platforms could not be set up:
* device_tracker.tado

Testing the configuration returns no obvious issues though:

$ hass --script check_config
Testing configuration at /home/homeassistant/.homeassistant

Looking in the directory of my local home assistant installation the required tado.py file exists and looks fine.

What are the best steps to troubleshoot an issue like that?