Why every cell of my costmap is considered free?

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Hi, I am writing a Global Planner plugin in C++ and I am having the following issue processing the data incoming from the costmap_2d generated by move_base: every cell of the map is marked as free even if that's not the case (I am using a gazebo environment from Turtlebot3 packages, turtlebot3_stage_4). This is obviously a big problem when I try to generate the path inside the code, since the planner can not discriminate between free, occupied and unknown space.

Also, consider that the map is not static, but is generated using SLAM with gmapping method.

Could anyone suggests what may be wrong with these configuration files? I have been dealing with this problem for some time now and I really can not find what is wrong.

costmap_common_params

footprint: [[-0.105, -0.105], [-0.105, 0.105], [0.041, 0.105], [0.041, -0.105]] 
footprint_padding: 0.01
robot_base_frame: base_footprint

update_frequency: 5.0
publish_frequency: 5.0
transform_tolerance: 0.5  #0.2
map_type: costmap

obstacle_range: 3.0
raytrace_range: 3.5

plugins:
 - {name: obstacles_layer, type: "costmap_2d::ObstacleLayer"}
 - {name: inflater_layer, type: "costmap_2d::InflationLayer"}

# Layers
obstacles_layer:
 observation_sources: scan
 scan: {sensor_frame: base_scan, data_type: LaserScan, topic: scan, marking: true, clearing: true}
  track_unknown_space: true
 footprint_clearing_enabled: true
 combination_method: 1

inflater_layer:
 inflation_radius: 1.75
 cost_scaling_factor: 2.58

costmap_global_params

global_costmap:
global_frame: map

static_map: true
rolling_window: true
resolution: 0.05

costmap_local_params

 local_costmap:
  global_frame: odom

  static_map: false
  rolling_window: true
  resolution: 0.05