Hey all, thanks for the help. I apologize for not responding, I subscribed to this thread but must have done it wrong and never got any email notifications. After this post, I found GPU Lightmass and gave that a try. Using the GPU did not result in these corrupted lightmaps. The GPU tool is more complex to use, but I believe I can make that work and get good results.
Since then, I moved from 4.24 to 4.25. Created a brand new map, and using standard/CPU lightmass, I ended up with the same corrupted lightmaps. The skysphere mesh has cast shadow disabled by default, so that was not the culprit. There are also oddities like spots where it looks like an invisible object is casting a shadow, but I am certain there is no object there. Here’s a picture:
This is a fresh map with mostly BSP. I am 100% sure nothing is there, haha
Some part of me wants to blame my specific CPU. I have a relatively old Haswell-E 8 core i7-5960x. For now I will be relying on GPULightmass. I also have other team members that can build my lighting for production if need be. I’m still open to solutions or ideas for testing if anyone can think of anything. Thanks again!