Reproduction steps:
1. Download "unityTerrainAssert.zip" project and open in Unity
2. Enter Play mode
3. Walk forward with W to the door and press ctrl

Expected: no error shows up in the console
Actual: error appears in the console

Reproduced on: 2017.2.0f1; 2017.2.2p1; 2017.3.2f1; 2018.1.0a5
Note reproduced on: 2017.2.0b1; 2017.2.0b11
Regression introduced: 2017.2.0f1

Note:
Error message - "Assertion failed: Assertion failed on expression: 'j - i == terrainChunksInfo.numChunksInX * terrainChunksInfo.numChunksInY'
Assertion failed: Assertion failed on expression: 'false'
Assertion failed: Assertion failed on expression: 'false'"
On 2018.1.0a6-2018.2.0a5 versions after pressing ctrl Unity editor freezes
On 5.6.5p3-2017.1.3p2 versions Unity crashes while opening project