/mavlink/to topic does not publish anything

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Hello

I'm using px4 + gazebo for SITL simulation

Running as follows:

px4: no_sim=1 make posix_sitl_default gazebo_iris

gazebo: roslaunch gazebo_ros empty_world.launch world_name:=~/catkin_ws/src/gazebo/worlds/iris_fpv_my_cam.world gui:=$1

Actually, my simulation works fine - using an OFFBOARD mode, I can control the drone during simulation.

The problem

1. When trying to look into communication from MAVROS-node into px4 - i get an empty stream. (using rostopic echo /mavlink/to )
2. On the other hand, if I look into the communication from px4 to MAVROS, i get a stream full of mavlink messages (using rostopic echo /mavlink/from), which is good.

Any idea why there are no messages from MAVROS to px4 but there are from px4 into MAVROS?