Problem baking 4096 Lightmaps (2048 bake fine) - please help!

I am getting a very strange issue when trying to bake my lightmaps.

They used to bake fine, but I upgraded my version of Unity, then changed a few meshes, and now I'm seeing the following...

• With map resolution set to 2048, the scene bakes fine in about 5 minutes.
• With mp resolution set to 4096, the scene stalls and never finishes (the timer actually just goes up and up and up...)

When baking at 2048 I noticed that the lightmaps appear in pretty good shape as they render. See the foreground huts are baked, and the wall behind it is flat...


At 4096 everything goes black, the background wall bakes first, and looks really weird...


Any ideas what I might do to fix this?
Thanks,
Dan

 

Update - checked the project in Unity 2018.2.19 and it bakes fine. Looks like something is busted in the new 2018.3.10. Great.