Steps to reproduce:

1. Make sure that you have iOS platform support installed
2. Download and open the attached project
3. Enable Compress Lightmaps toggle in the Lighting Settings window
4. Set Directional Mode to Directional
5. Generate lighting
6. Observe the artefacts

Notes:

- Only reproduces when using Directional lightmaps + lightmap compression
- Reproduces with all Lightmap Encoding Quality presets
- The issue can be mitigated by overriding the texture format manually
- Tested using: 2018.4.20f1, 2019.1.14f1, 2019.2.21f1, 2019.3.9f1

For more information please refer to the following Favro card: https://favro.com/organization/c564ede4ed3337f7b17986b6/0ae5422e2f78207a0998ab80?card=Uni-134829