Where does RViz/MoveIt get the link position

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I'm currently trying to get the universal_robot package with UR5 running in Gazebo and RViz under Melodic (see also https://github.com/ros-industrial/uni... ).

In the issue above I have the problem that the robot which is shown in RViz looks broken and all the link positions are set to 0,0,0 whereas the /tf topic seems to be fine:

Here my general understanding question: Which topic is RViz using to calculate the link position? In the screenshot above the links are all in 0,0,0.

I guess the process is somehow like this:

Gazebo -> /joint_states -> /tf -> RViz magic topic