To reproduce:
1. Open attached project;
2. Open "Town" scene;
3. Make sure Api Compatibility Level is set to .NET 2.0 (Edit > Project Settings > Player Settings > Configuration);
4. Open Arduino IDE;
5. Open "LED_Color.ino" sketch;
6. Add Library "SerialCommand.h" (Sketch > Include Library > Add .ZIP Library...);
7. Connect Arduino Uno to your machine;
8. Make sure Board is set to Arduino/Genuino Uno (Tools > Board);
9. Make sure that correct Port is selected (Tools > Port);
10. Make sure that SerialPort in the Arduino sketch is the same as the one in the 'ArduinoController' script (line 28);
11. Press "Upload" in Arduino sketch;
12. Enter Play mode in Unity Editor.

Expected result: no crash when using Arduino with Oculus Rift.
Actual result: crash in Terrain::Transfer<JSONWrite> when using Oculus Rift and Arduino

Reproduced on versions: 5.4.0f3, 5.4.1f1.
Not reproduced on versions: 5.4.1p1, 5.5.2p4, 5.6.0f2.