The blur is because the vehicle was vibrating. It means the thrusters were on. Note how they smooth out shortly after deceleration stops. Some of the larger movements could be maneuvering. If it is orientating itself then the antenna would intermittently move back and forth relative to the receiver.
I was thinking vibration but wouldn't we see a change when the retro-thrusters hit halfway through? I'm assuming the first part with downward slope is the craft accelerating due to gravity?
Given it's a polar landing I don't know how to translate this to the velocity vector of the lander.
