The collider will not be generated .

[liuxinjia]

When the set the colliderLODIndex in TerrainGenerator to another number instead of 0.
The collider will not be generated.

[liuxinjia]

The UpdateCollisionMesh function whether can be called is decided by UpdateTerrainChunk function. If the mesh LOD index is different from the collidererLODIndex the mesh still can be generated but mesh collider will not be assigned to. We need to UpdateCollision by ourselves.

[WoodingMP]

Aware it's been a long time since this was reopened but just had the same issue myself after finishing episode 21, the solution I found was by adding a call to UpdateCollisionMesh() at the bottom of TerrainChunk.OnHeightMapReceived(...)

Sebastian mentioned in the video to add UpdateTerrainChunk() so that your first chunk gets loaded in correctly despite not moving, but he didn't mention about the collision mesh. Hopefully this helps anyone else who comes across the same problem!