To reproduce:
1. Open attached project
2. Open scene "AnimationTesting"
3. Enter play mode - notice that the sprite twitches in position sometimes (into the ground, where it should not appear)

Pausing the play mode and moving frame by frame can provide a better look on the problem

Explanation: The problem is that the sprite changes in a single frame, while the translation is a curve and change over a certain time. So sometimes, during playback Sprite and position are de-synced.
To fix, simple use Constant tangents on your position curve.