Reproduction steps:

1. Open "MinimalRepro" project
2. Enter Play Mode
3. Hold "A/D" or the "Left/Right Arrow"
4. See that the Console outputs "-1/1"
5. Press "Left Shift" to change the Scene
6. Notice that the Console outputs "0"

Expected Result: The Input stays the same as before loading a new Scene
Actual Result: The Input resets after loading a new Scene

Reproduced with: 2018.1.0a3, 2017.3.0a8, 2017.2.0p1, 2017.1.2p3, 5.6.4p2

Note:
Scenes are not loaded Additively