robot_state_publisher publishes strange tf

edit

I tried to develop simulation environment for ROS2.
https://github.com/atinfinity/megarov...

And, I launch the following command.

ros2 launch megarover_samples_ros2 vmegarover_with_sample_world.launch.py

This launch file uses robot_state_publisher to publish tf.
But, it seems some frames publish strange tf.
So, I launch the following command to check tf.

ros2 run tf2_tools view_frames.py

As a result, I found that some frame has Wall Time as time stamp.
But, I don't know the reason.