large difference in speed between add pointcloud to octomap and remove it from the octomap

[dbdxnuliba]

Your environment

• ROS Distro: |Noetic]
• OS Version: e.g. Ubuntu 20.04
• octomap-1.9.8
  *octomap_ros-0.4.1

As shown above gif ,
1)when the object point cloud appears, the octomap of the original non-occupied part is updated to the map of the occupied part very quickly,and it seems good;
2)but the question is when the object point cloud moves away, the map of the original occupied part should be updated to the non-occupied part, but we can see It is very slow to update the non-occupancy part.
3)and the delay time is about 2 seconds between point cloud disapper and octomap update to non-occupancy state in rviz , is this a bug,how can we improve it ?

and the point_cloud_topic frequency is 6 hz,

Question :
1)Why is there such a big difference in speed between add pointcloud to octomap and remove it from the octomap
2)how can we speed up the process about when the object point cloud moves away, the map of the original occupied part update to the non-occupied part