A user encountered an issue with Landscapes not rendering once baked with GPU Lightmass. The user was using Ray Tracing. If using normal CPU Lightmass baking, landscape remains the same.
Result: Landscape renders all black once bake has completed
Expected: Landscape remains properly lit once bake has completed
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-199910 in the post.