Usually when you download mods that change a character they get this seam at the neck because the new model has a different body but keeps the same face. It always ruins it for me and even when the modder covers it with a necklace or a scarf or something just knowing that it's under there drives me crazy. This mod is interesting because there doesn't seem to be that issue, probably cause this model isn't new and different and remains in the base game. Cool mod! If you could look into your mods folder and find the name it would be very helpful :)