I think I’m going crazy. I have this very simple model with rounded elements. Geometry is clean, smooth is on, sharp edges checked, auto smooth checked, custom split normal data cleaned, normals are ok. And yet in UE4 I see this:
Import and export settings are the same for all my assets and exept for this one everything is ok.
What else can I do?
This could be related to UV and lightmap baking rather than normals.
UE4 uses lightmaps (it bakes lighting to textures). Have you created a second UV set for the lightmap? If you have, check that the curved part is not split into multiple UV islands, or this could create sharp changes in the lighting between polygons.
If you don’t have a second UV set, you should create one, or Unreal will do it for you with an auto unwrap and you will have no control.
I usually let Unreal generate lightmaps for me
OK, then it’s unlikely to be because of the UVs. Still, from your image, I have some doubts that the normals are actually flat. If you look at the left side of the first image, that part doesn’t seem flat shaded.
But this should be testable. If you look at the object under a different lighting (create a new moveable point light in Unreal and bring it close to the problematic area), does it still look flat shaded? If it still looks flat, then you will know the problem is really in the normals. If it looks smooth, the problem is likely in the lighting.
If the problem really is flat shading, you would have to check both the export settings in Blender and the import settings in Unreal (I believe there are some options that recalculate normals on import).
In Blender, I normally export to Unreal using the FBX format and this setting has been working fine for me:
I don’t have access to Unreal at the moment, but I know there is a setting for how to treat normals when importing an object.
I can think of an other possible cause. Does the object have a normal map on its material, especially a large scale one that’s been baked to the object’s shape? I say that because Unreal uses a different kind of normal map than Blender. If you brought a normal map from Blender in Unreal, you have to flip the green channel. There is an option to do it inside Unreal, you just have to double click on the texture and use the search bar to find the “flip green channel” checkbox.
I use edge in smoothing settings too, and I also use Substance Painter for my textures with UE4 export settings. This actually gave me an idea and I looked on SP baked maps, and AO map has this edges on it:
I tried to detach normal and AO map in UE earlier, and I think those edges were still there, but I`ll better check it again
Sometimes “reset normals” in the mesh buttons can fix things. Especially with imported mesh objects.
Is it in blender or in ue4?
Sorry I meant reset vectors. Mesh >> Normals >> Reset Vectors.
Nope, didn`t work. Also, I made a completely new mesh with the same element, and it has the same problem 
