Nav2 bringup does not start slam_toolbox

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Hello,

I tried to launch the nav2 bringup launch file (Ubuntu 20.04, ROS2 Foxy) like this:

IncludeLaunchDescription(
PythonLaunchDescriptionSource(os.path.join(get_package_share_directory("nav2_bringup"), 'launch', 'bringup_launch.py')),
launch_arguments={
  'namespace': 'robot1',
  'use_namespace': 'True',
  'use_sim_time': 'True',
  'slam': 'True',
  'map': '',
  'params_file':os.path.join(ess_path, 'launch/slam_and_navigation', 'nav2_params.yaml'),
  'default_bt_xml_filename':os.path.join(get_package_share_directory('nav2_bt_navigator'), 'behavior_trees', 'navigate_w_replanning_and_recovery.xml'),
  'autostart': 'True',
}.items()),

Gazebo and a robot, spawned with the gazebo_spawner of nav2 is running in the background. For some reason, the slam_toolbox does not seem to get started. I have not edited or done anything else.

Do you have any ideas?

Thanks