Points moving in calcOpticalFlowPyrLK() although camera is stationary

Hi, I am attempting to do tracking in ROS. I used this function but the points turned out to be constantly moving even though my camera is stationary…
calcOpticalFlowPyrLK(img_l_0, img_r_0, points_l_0, points_r_0, status0, err, cv::Size(21,21), 3, cv::TermCriteria(cv::TermCriteria::COUNT+cv::TermCriteria::EPS, 30, 0.01), 0, 0.001);

Using a D455 Realsense stereo grayscale