Frame stuttering after keyframing

Hi everyone,

I'm having a problem with a current editing project – I've attached the relevant footage.
It involves tracking the person in the frame as they stand up and sit down, and I'm setting two keyframes for this.
However, the image stutters slightly at the beginning and towards the end. I haven't had this problem in previous projects with the same setup; I can't figure out what's different about this file compared to previous ones that could be causing this stuttering.
Restarting didn't help. Does anyone have any ideas? Am I missing something?

Thank you!