Hi, I have created a very simple level with only one mesh (excluding the water plane), which was created from the engine’s Cube with Cube Grid and Poly Cut.
I only have two light sources, a directional light, which is also the Sun light, and the Sky light, which are all set to moveable, in the level.
When I was changing the Sun angle, I found strange shadows coming from nowhere on the mesh:
I have tried changing the mobility of the lights (and building the lights), disabling and enabling lumen, but none of them could solve the problem or even mitigate it.
I really could use some suggestions on possible causes of this problem and I appreciate all replies and your time in advance
I suspect a problem with the UVs. There are some tools for working with UVs in Modeling Mode. Do you see any difference in the shadows if you try ‘Unwrap’ or ‘AutoUV’?
First I’m sorry for my late reply. I was busy the last two days for an assessment and didn’t have time to use Unreal.
Thanks for your reply. I have checked the UV map, and found that the UV is overlapping, probably messed up by the modelling tools. After applying AutoUV and regenerated the lightmap UV, the shadow on the left now disappears, though that one on the right still persists.
I think I may need to use multiple simpler meshes to build the scene rather than with one single mesh cut and modified from the cube. Or I may try to learn to use some external modelling tools to create a new one.
First I’m sorry for my late reply. I was busy the last two days for an assessment and didn’t have time to use Unreal.
Thank you for your suggestion. I have little knowledge with normal/tangent maps, but I tried to apply the material to a single cube and place the cube around the same spot as the mesh and no strange shadows are on it.
I think, as Astrotronic points out, the problem probably is caused by UVs. I will try to look into this problem more later, after I complete some exams
No problem with the late reply, but let me insist on the fact that it was a normal issue and not a UV one. The fact that you use the same material on another mesh and everything is fine tells me that the problem was on the geometry itself.
UVs do not cause those kind of artifact they affect the textures only (Therefore, not the light bouncing on the surface of the geometry)
It could happened if you normal map is broken, but it would look worst than that and the problem would be consistent from one mesh to another.
The easy fix would be to go in Blender and clic on Shade Flat and see if it fixe your issue
I was thinking about lightmap UVs, (the UVs used for shadows in baked lighting) because I’ve seen unexpected shadowing as a result from close/overlapping lightmap UVs.
Krimsons suggestion of looking into geometry normals is good. You might not need to export to Blender either. Under the ‘Attributes’ section of the Modeling Tools you can recompute Normals. (experiment with ‘Normal Caluclation Method’ and ‘Split Normal Method’)
Now it’s clear! After importing the asset as FBX into Blender (it’s also my first use of Blender ) I immediately noticed that its normal was not right. Thank you KrimsonGames. Your insist was awesome!
Fortunately, the solution provided by Astrotronic worked perfectly. After changing the option of Split Normal Method to “Face Normal Threshold”, all strange shadows disappeared, regardless of how I changed the angle of the Sun light.
It is amazing to learn from your helps and suggestions. I really thank both of you. I will mark KrimsonGames’s answer as the solution, though it’s quite a shame that I cannot mark both of yours.
) I immediately noticed that its normal was not right. Thank you 
