Objects with Receive Global Illumination set to Lightmaps have a lighting solution with lightmaps for baked direct and indirect lighting, and lightmaps for Enlighten Realtime Global Illumination. For more information about Receive Global Illumination, see the Mesh Renderer settings and the script reference for ReceiveGI.
When you use Unity’s LOD system in a Scene where you have enabled Baked Global Illumination and Enlighten Realtime Global Illumination, the system lights the most detailed model out of the LOD Group as if it has the Contribute Global Illumination setting enabled and isn’t part of the LOD group."
Enlighten Baked Global Illumination can only compute direct lighting for lower LODs and the LOD system must rely on Light Probes to sample indirect lighting.
To enable the Editor to produce lightmaps with Enlighten Baked Global Illumination or Enlighten Realtime Global Illumination, select the GameObject you want to affect, view its Renderer component in the Inspector window, and ensure that Contribute Global Illumination is enabled.
For lower LODs in a LOD Group, you can only combine baked lightmaps with Enlighten Realtime Global Illumination from Light Probes or Light Probe Proxy Volumes, which you must place around the LOD Group.