The only that does something positive is Reset Hard Normals in Edit Attributes, reduced this issue by a lot(not everywhere)but not completely. Seams on some flat surfaces still present.
It’s a little hard to tell exactly what’s going on with the screenshots you provided, but it looks to me like a triangulation / normals issue. Is this issue happening where you have non-manifold geometry? Unreal needs to convert quad meshes to triangulated meshes on import- my guess is it was not able to correctly interpret the geometry during this conversion resulting in bad geometry and a hard normal line. Try triangulating your mesh directly in Blender so you can directly check for any normal issues, then import that version of the mesh into Unreal.
Also, make sure your smoothing groups are correct on the mesh before you import it to make sure all of your vertices are set to smooth.
You can also try selecting “Loose Geometry” in Blender to make sure you don’t have any floating edges, faces, or vertices.
It was a Blender case, never noticed because Blender’s default for viewport “Studio Shading” mode which everyone uses by default is showing the perfect surfaces and none of shading.
Found an easy fix which solves entire problem with one click in this good video:
He selects in viewport shading MatCap, which reveals shading issues very well, better then any your texture you have(especially if you select horizontal or vertical dynamic strips).
The thing that fixes it all is called Weighted Normals.
