This appears to be a bug that was introduced in 4.26. The same meshes in 4.25 do not produce any errors. I manually checked and there are no double faces, no inverted faces, all normals are correct and there are no other issues with the mesh. uvs don’t make a difference either. no matter if created within unreal or using imported ones. I do use blender (fbx export) but also get the issue with objects exported from 3dsmax previously. This is only affecting Automative Materials and it disappears when turning off flakes and orangepeel (in carpaint material). in the metal material on the other hand it looks correct if use object uvs is turned on.When the object in question is rotated the faces that turn black change (like flickering - definitely looking like a broken mesh but definitely isn’t the case). at some angles it even looks correct.