How to reproduce:
1. Open the attached project ("case_1190096-Project.zip")
2. Open the SampleScene in the Scenes folder
3. Enter the Play Mode
4. Press the controller's "Left Stick" and the keyboard's "A" Key at the same time

Expected result: There are no errors thrown
Actual result: Errors are thrown

Reproduced in Unity versions: 2019.2.9f1, 2019.3.0b6, 2020.1.0a8
Reproduced in Package version "preview - 1.0.0"

Couldn't test with Unity versions: 2017.4, 2018.4 (Problems with the Package Manager)
Couldn't test with Package versions lower than "preview - 1.0.0" (There's no InputActionMap.FindAction function)

Note: Exception "Should not get here" is thrown on any input from the controllers after the "IndexOutOfRangeException".