Random assertion failure

So I recently updated to the Unity 2017.2 Beta and now a line of of code that worked perfectly fine ends up generating (seemingly randomly) errors.
The line of code is: GetComponent<Rigidbody>().rotation = Quaternion.Euler (0.0f, 0.0f, GetComponent<Rigidbody>().velocity.x * -tilt);

and the errors im getting are:

Assertion failed: Assertion failed on expression: 'CompareApproximately(det, 1.0F, .005f)'
Assertion failed: Assertion failed on expression: 'fRoot >= Vector3f::epsilon'
Assertion failed: Quaternion To Matrix conversion failed because input Quaternion is invalid {-1.#IND00, -1.#IND00, -1.#IND00, -1.#IND00} l=-1.#IND00

Im not sure what exactly causes the errors because often the code runs fine and the other time it end ups with the mentioned errors. If I replace the line of code with

GetComponent<Rigidbody>().rotation = Quaternion.Euler (0.0f, 0.0f, 0.0f);

aka replace “GetComponent().velocity.x * -tilt” with any number no matter if negative, positive etc. the error stop appearing. So i added

Debug.Log()GetComponent<Rigidbody>().velocity.x * -tilt);

before the line of code to see if “GetComponent().velocity.x * -tilt” generates any strange values but they all seem fine to me. I also cant find like any pattern (like only negative numbers causing the error or anything like that). I already re-imported all assets and I read that someone fixed a similar problem by recreating animation controllers, but i don’t have any . I attached the Log File of the Unity Editor to my post and hope that anyone maybe knows whats causing the error.

Did you figure this out?