So you’re applying the material(s) in UE after import? The import settings show the Textures / Materials is disabled. It’s not that it’s a bad idea to do so, but it could help in identifying the material made in UE as having problem(s). Another potential cause is the LOD, and yet another is the mesh distance field of one or more of the meshes in question. I don’t see how 0.5 level scale would yield accurate results everywhere else in the scene except the one corner, but I suppose it’s possible. You shouldn’t have to reduce your static level scale to 0.1 simply to get rid of an artifact in the corner while everything else displays well. I’m not disagreeing that it’s a potential cause, but simply stating how absurd it is to fix an artifact by using what’s become a standard which is rather divergent from the engine’s other capabilities too. I’ve had no artifacts of the kind on a likely slower and less RAM / graphics capable computer without lowering static level scale to 0.1 or even 0.5, and in fact have encountered artifacts by doing so. When you lower level scale, it is commonly thought that quality should be increased and smoothness decreased by a certain amount (to 0.6-.75), and I’ve seen the video and read through the Powerpoint presentation about it. It was an example scene which could be quite different from lots of other archviz scenes, and I’ve heard that increasing smoothness with lowered level scale is effective at getting good results too. So, it’s important to be wary of being so frugal with adjusting World Lightmass settings, not knowing in particular how it’s going to affect the scene with its other settings for the lights, materials, and post process. In other words, erring on the side of caution is probably a better approach.
I really think you’re much better off checking the material(s) and meshes of the problem corner there in terms of LOD settings, distance field representation, and adjusting ambient occlusion in its various types to try and fix it. The outer-facing corner is probably not an issue because it doesn’t have ambient occlusion attempting to account for a difficult to calculate area. The inner corner is receiving no occlusion other than how the corners of the walls and ceiling meet, so the potential is there to get insufficient ambient occlusion calculation, resulting in the distorted shadow.
As far as UVs, you can try disabling “Generate Lightmap UVs” on import, and then generate the lightmap for those meshes in the UE mesh editor after re-importing. You need to re-import because the lightmap UV data is attached to the ones that were imported and are used in the picture. I don’t see all the import settings in the screenshot. Are there more when importing those meshes, or is that the entire dialog of settings you saw?