To reproduce:
1. Open attached project
2. Press and hold A and click
3. Notice that the sword animation looks weird (.gif added to edit), but it doesn't in 5.3
This happens because of the line 242 in FitAnimator.cs:
effects.transform.rotation = new Quaternion(effects.transform.rotation.x * -1.0f,
effects.transform.rotation.y,
effects.transform.rotation.z,
effects.transform.rotation.w * -1.0f);

If the line is commented out, everything behaves the same in all tested versions.

Reproduced on: 5.4.0f2, 5.5.0b9, 5.6.0a1
Not reproduced on: 5.3.6p5