If it's normal map related: The only way to 'fix' the seams created from model detachment is to bake the normal map from a highpoly source to a low poly model that already has the seams in-place. This way, the normal map is working with the seams rather than trying to act like they aren't there. While it most likely won't remove it 100%, it should reduce the visibility of the seams. If it's not normal map related, there's nothing you can do except not segment.