I’ve had these problems also until now.
I discovered there may be multiple causes to this.
- Lightmap Resolution
Yes, it may be as simple as that. The lightmap resolution of a mesh is set to 64 by default, which is insufficient for a larger object. Try going to the static mesh options and setting it higher and see how it goes. Also, make sure that the resolution is not overridden in each the static mesh instance options.
- Incorrect Normals
Make sure that all your normals are facing the right way. Try recalculating normals inside of your modeling software.
Then, if you import your mesh and you get an error saying that there are no smoothing groups, that usually means that Unreal didn’t get all the normal information about the mesh. Try to export the mesh with different settings (edge smoothing, face smoothing, normals only, etc.). If it still doesn’t work, try an older version of the export plugin (for FBX, especially).
If it still doesn’t work, go into the static mesh options (in Unreal) and try checking/unchecking Recompute Normals and Recompute Tangents and see how it goes.
- Extreme Lightmap World Settings
If none of the above worked, you’ll have to look into Lightmap options under World Settings. If you have set crazy values in there, it may generate lighting artifacts.Try to copy these values from an example project that you see in the example tab, like the RealisticRendering project. This will initialize your lightmap settings with values that have been tested and are known to work.
- Low Lighting Quality
Finally, if you still have small lighting artifacts, it may be that you have to build lighting at a higher quality. You can set the different lighting quality options when you click the small arrow near the Build button.