A couple things:Make sure mesh normals are exported from your 3d app (not just smoothing groups)Make sure the tangent space is set to the same as where you baked your normal map. You can set the tangent space in the mesh object's properties. You can also set a default tangent space in Edit->Preferences, though this will only apply to newly imported meshes.
i think this could help ... yes this artifact happens when you have overlaped uvs island so u can solve it by1- make sure that u gave every uvs island a diffrent( smoothing group or phonge break) even if they are have overlaping uvs.2- export normals of the low poly mesh from the applicaton (object with normals )3- make sure u added enough edge padding to your uvs.4-make sure u dont have fliped uvs while ur ovelaping them.5- when u baking make sure that the heigh poly is full model and the low poly is full model with normals . and then bake. these is important and can cause normal proplems like these onesnote : if the normals is right... it renders right in any applicaton .its not the applicaton proplem.if it didnt work try not to overlap the uvs ...i know this is stupid option and doesnt save uv space but at least u can know if the uv overlaping is the proplemi hope that is helpfull and solve your proplem. and reply if it works