How to reproduce:
1. Open the attached project
2. Open and play Scene
3. Move the character with arrow keys to one direction
4. Stop and start moving again
5. Notice the spikes in the screen (Red graph on the screen indicates Animator.velocity.magnitude. Press space key to apply correction)
6. (workaround) Multiplying ratio of lengths (AnimatorStateInfo.length) of current and previous frames seems to correct the problem. Press Space in playmode to see this result

Note: tested using simple animation controller (without blend trees). It works fine