Gazebo7 hangs with black screen while "Preparing your world"

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Hi,

I'm really stuck with the this problem and need help to figure out what's wrong...

I've set up two identical laptops (Dell XPS 13) in an identical way (Ubuntu 16.04 Gnome, ROS Kinetic). I've installed sudo apt install ros-kinetic-care-o-bot on both laptops.
Now I source /opt/ros/kinetic/setup.bash and then run roslaunch cob_bringup_sim robot.launch robot:=cob4-7 robot_env:=empty on both machines, i.e. only using latest release of the related packages.

While gazebo shows up the Care-O-bot with two arms on laptop A, gazebo stays black on the other laptop B (even after waiting a while to allow downloading additional models) and keeps showing the splash screen "Preparing your world..." forever.
Ironically, both laptops successfully show the Care-O-bot base when running roslaunch cob_bringup_sim robot.launch robot:=cob4-3 robot_env:=empty (base-only configuration) from debian packages.

I've already swapped the SSDs between the laptops to verify it's not a hardware (RAM, GPU,...) issue:
The simulation stays black for cob4-7 using SSD B in both laptop A and laptop B - while simulation of cob4-3 works usinging SSD B on both laptop A and laptop B.
I've also already re-installed gazebo, ros various other packages...nothing gained.

One thing I saw is that ~/.gazebo/ogre.log on SSD A shows entries like:

17:36:46: Added resource location '/opt/ros/kinetic/share/cob_description/meshes/cob4_torso' of type 'FileSystem' to resource group 'General' with recursive option
17:36:46: Initialising resource group General
17:36:46: Added resource location '/opt/ros/kinetic/share/cob_description/meshes/cob4_arm' of type 'FileSystem' to resource group 'General' with recursive option
17:36:46: Initialising resource group General
17:36:47: Added resource location '/opt/ros/kinetic/share/cob_description/meshes/drive_wheel' of type 'FileSystem' to resource group 'General' with recursive option
17:36:47: Initialising resource group General
17:36:50: Added resource location '/opt/ros/kinetic/share/cob_description/meshes/cob4_base' of type 'FileSystem' to resource group 'General' with recursive option
17:36:50: Initialising resource group General
17:36:50: Added resource location '/opt/ros/kinetic/share/cob_description/meshes/cob4_head' of type 'FileSystem' to resource group 'General' with recursive option
17:36:50: Initialising resource group General
17:36:50: Added resource location '/opt/ros/kinetic/share/cob_description/meshes/sensors' of type 'FileSystem' to resource group 'General' with recursive option
17:36:50: Initialising resource group General
17:36:52: Texture: com.png: Loading 1 faces(PF_R8G8B8,200x100x1) with 5 generated mipmaps from Image. Internal format is PF_X8R8G8B8,200x100x1.
17:36:54: Texture: spot_shadow_fade.png: Loading 1 faces(PF_R8G8B8,128x128x1) with 5 generated mipmaps from Image. Internal format is PF_X8R8G8B8,128x128x1.
7: Added resource location '/opt/ros/kinetic/share/cob_description/meshes/cob4_torso' of type 'FileSystem' to resource group 'General' with recursive option
17:36:47: Initialising resource group General
17:36:47: Added resource location '/opt/ros/kinetic/share/cob_description/meshes/cob4_head' of type 'FileSystem' to resource group 'General' with recursive option
17:36:47: Initialising resource ...