If an Animator clip has a Steer Local Rotation value that is not zero, then when the cutscene is previewed, and the preview is stopped, the character will have a rotation that is a multiple of 360-degrees above or below its original value. If this value keeps increasing/decreasing, I presume this could cause problems of floating-point accuracy.
On an unrelated note… is there any chance you can change the code formatting on these forums? On Chrome, hovering the mouse over a code area causes it to flicker and resist selection. On Edge, hovering the mouse causes code to disappear completely.