Lightmaps are corrupted and covered in artifacts with 'terrainInstanceHashes.find (it->instanceID) != terrainInstanceHashes.end ()' errors when there are multiple low poly meshes in the scene.

1. Open the attached project 'Lightmap'
2. Open the available scene
3. Enable 'Meshes' in Hierarchy
4. Build Lightmaps
Note: After build, terrain lightmaps are corrupt and covered in artifacts
5. Disable 'Meshes' in Hierarchy
6. Build Lightmaps
Note: Lightmaps are generated fine