AR tag frame from the package ar_track_alvar is moving in RVIZ although it should be static

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Hi I have frames issue. I installed ar_track_alvar package and I started gazebo. The AR tag has no movement in the scene. However in RVIZ, its frame moves.

Which lead to inaccurate measurements of the distance of the tag with respect to the camera frame. Which can be seen in the following image.

Although, it should be close to the pose of the ground truth of the quadcopter because the tag is on the ground. (See this image)(http://)

Please can someone tell me why the frame is moving while it should not move Thanks in advance