2012 Mercedes Benz E250 Gearbox

I have a Mercedes Benz E250 which I have bought in Malaysia in 2012. The car is experiencing some problem whenever I apply brake on the car. The rpm meter normally should go down smoothly when car is slowing down. However, in my case the rpm meter fluctuates up and down (unstable) when the car is decelerating or when I apply brake. I could feel some minor jerk when braking. I have sent my car to the authorized mechanic to run diagnostic check but they found no issue with the car.

I greatly appreciate if you could offer your professional diagnosis to solve my car issue.

Thank you very much