Another important note is that it’s not just a matter of the Lightmap resolution, but how the lightmap is calculated through lightmass. It has some similar functions to other raytracing tools found in 3ds, how photons are bounced, calculated, approximated, etc. There’s a bunch of write-ups on this. I tend to like this one HERE. But even then, your UV map for the lightmap is problematic, leading to…
Steamroller’s got it’s pros and cons, but I don’t typically use it for any key meshes, including walls and buildings. I’ve worked a lot with models coming from Revit -> 3ds Max -> Unreal. Revit is a pain, and it’s almost not worth trying to fight the welding too much. However, the technique for UVUnwrapping should still be the fastest way to create an even lightmap distribution. I use it for all sorts of things that are geometrically complex, but need to have the lightmap calculate the same across it. But if you have your coplanar faces (the ones in my image selected in red, they are all next to eachother) scattered and rotated all over the UV map, you’ll likely always see this.