Running a sample application with ROS Melodic and Gazebo 9

I am following this tutorial in the RoboMaker Developer Guide. After building the base image, the robot image and the simulation one, I have runned the robot application with the following command:

$ docker run -it -e DISPLAY -v /tmp/.X11-unix/:/tmp/.X11-unix/
-u robomaker -e ROBOMAKER_GAZEBO_MASTER_URI=http://localhost:5555
-e ROBOMAKER_ROS_MASTER_URI=http://localhost:11311
helloworldsampleapprosmelodicgazebo9robotapp:latest

and the simulation application with this other:

$ export DISPLAY=:0

$ xhost +

$docker run -it -e DISPLAY -v /tmp/.X11-unix/:/tmp/.X11-unix/
-u robomaker -e ROBOMAKER_GAZEBO_MASTER_URI=http://localhost:5555
-e ROBOMAKER_ROS_MASTER_URI=http://localhost:11311
helloworldsampleapprosmelodicgazebo9simapp:latest

In order to visualize the simulation application in Gazebo9 I have entered into the simapp image and run the gazebo client with the following commands:

$ docker exec -it bold_babbage bash

$ cd /home/robomaker/workspace/aws-robomaker-sample-application-helloworld-ros1/simulation_ws

$ source /opt/ros/melodic/setup.bash

$ source /usr/share/gazebo-9/setup.sh

$ source ./install/setup.sh

$ rosrun gazebo_ros gzclient

The Gazebo GUI opens inside the Virtual Desktop but the robot stands still instead rotating around the z axis with angular velocity 0.1 rad/s. I obtain the following messagge:

[[ INFO]] [[1654096062.809673647]]: Finished loading Gazebo ROS API Plugin.

[[ INFO]] [[1654096062.821667855]]: waitForService: Service [/gazebo/set_physics_properties] has not been advertised, waiting...

Do you know what could be the cause of this problem?