Error when following Husky Dual UR5 Mobile Manipulation Demo (Simulation)

[stevensu1838]

Hi,
I've been following the Husky Dual UR5 Mobile Manipulation Demo (Simulation) tutorial. And I am on Controlling The Grippers session. I could control the gripper with no problem by running the following commands:
$ roslaunch husky_gazebo husky_empty_world.launch
$ rosrun robotiq_s_model_control SModelSimpleController.py _topic:=/left_hand/command
typing “a” will activate the gripper, and then “o” will open it.

However, when I trying to load the robot in a more complicated environment instead of the empty world by the following:
$ roslaunch husky_gazebo husky_playpen.launch
$ rosrun robotiq_s_model_control SModelSimpleController.py _topic:=/left_hand/command
When typing “a” to activate it, both of the two arms and gripers disappear in Gazebo. Any chance you know what's going on and how to fix it?
The compaction is shown below: