Another big clue. I created another scene with just a grid of spotlights above a plane. With 4 spotlights enabled I bake, I see 4 light spots in the editor and all 4 work normally. If I increase to 8 lights and bake, I see 4 spots in the editor (on random lights) and only the lights with visible spots work. I tried increasing to 12 and 16, and always get 4 visible spots / working lights, at random locations.
