I enabled “Use emissive for static light” and set lightmap resolution to 4096 x 4096.
This is because your lightmass settings are very low and emissive alone is not really ideal for lighting a scene. Default unreal has standard lightmass settings and defaults to preview quality. Also it doesn’t look like you’re using a lightmass importance volume. This helps confine to photons to the location they are actually relevant.
- Firstly add a lightmass importance volume to your scene
- Change your lightmass resolution back down to something much lower. Default is 64x64, but feel free to go up to 512-1024.
- You could change the lightmass quality up to 2-3, smoothness to .75, and try a bake at a setting above preview.
Hopefully you get better results then. Adding a few lights will make a big difference though as it just adds a source of photons to process. I wish emissive was better on its own, but Iv found it needs some help from actual lights.