To reproduce:
1. Open the user's attached project using the EnvIronman VM (more information in Edit)
2. Open the SampleScene inside of the project
3. Go to Player Settings and set Scripting Backend to Mono
4. Build and run it

Expected: Notice the returned offset for "blendShapeParams" is 4, and all 6 values from the float array are shown:
blendShapeParams[0] = 10.23; blendShapeParams[1] = 11.33; blendShapeParams[2] = 22.23; blendShapeParams[3] = 33.23; blendShapeParams[4] = 44.33; blendShapeParams[5] = 55.33;

5. Close the player
6. Go to Player Settings again and set Scripting Backend to IL2CPP
7. Build and run it

Actual: Notice the returned offset for "blendShapeParams" is 8, and the printed float elements start from the second element, with the 6th one being 0 (uninitialized).
blendShapeParams[0] = 11.33; blendShapeParams[1] = 22.23; blendShapeParams[2] = 33.23; blendShapeParams[3] = 44.33; blendShapeParams[4] = 55.33; blendShapeParams[5] = 0;

Reproduced in 2018.3.0a1, 2019.1.14f1, 2020.1.0a2

Reproduced with Windows IL2CPP Player and UWP
Not reproduced with WebGL and Windows Mono