KLT Feature Tracker VPI sample code execution times difference

Hello,
1,2,3- sudo ./build/vpi_sample_06_klt_tracker cuda /opt/nvidia/vpi1/samples/assets/dashcam.mp4 /opt/nvidia/vpi1/samples/assets/dashcam_bboxes.txt

three times I execute KLT Feature Tracker VPI sample code same conditions, backend as cuda and logged each frame processing time. Each one is diffrent. some frame difference is more huge.

I expect it to be the same but not why?

platform is jetson xaiver nx jetpack 4.6.