Sorry for the late response. I solved part of the problem in Marmoset, I had the normal map affecting the diffuse as a layer in Painter so the seam appeared in the diffuse too and forgot to flip the green channel in Marmoset and to check Scale & Bias. I don't have problems with the shading anymore even if the seams can…
tangentspace normalmaps appear to be human readable but they are not. you can do some tinkering with them but what you are expecting is simply not possible with these maps. as Pior said, they are based on the lowpoly geometry, their tangents and UV orientation, previewing them as if they are a diffuse map will only lead to…
The OP mentions he had the TS normal affecting a diffuse layer, so even if the shading is correct in the normal, the color difference along seams in normals would still be visable in the color map. And aparently his G channel was inverted, which would cause a seam. He also mentions he found a solution here,…