robot model does not appear in rviz melodic

edit

I try to bring my robot model (which I have developed for kinetic) to work under melodic. Everything works so far (despite some plugin issues where I have already committed a pull request), but not the visualization of the robot model. The xacro description of the robot is here.

rviz visualization under melodic:

rviz visualization under kinetic:

Here are some points which I have investigated already:

• I've checked the model on the parameter server via rosparam get /amiro1/robot_description under kinetic and melodic and they are identical.
• The dae model is also valid, because rviz complains when I just manipulate the mesh location.
• The wired thing is, that the hokuyo dae mesh is visualized under melodic.
• I also check all rviz debug messages via rqt_logger_level and rviz tells me that the URDF description is loaded correctly.
• Maybe it is realted to this issue but again, the hokuyo dae is shown, but not my robot.

If one would like to test it, follow these steps:

1. checkout https://github.com/tik0/amiro_robot.git
2. checkout https://github.com/tik0/amiro_msgs.git
3. build and run roslaunch amiro_gazebo amiro_simple_world.launch

Can anyone help me with this issue?