How to bake different texture sets of one object properly?

jtdx8866

I have one character model and assigned a sub-multi material to it in 3Dsmax.  The head, arm, and body each have a separate UV sheet. I tried baking in substance painter, xNormal...   the normal looks really inconsistent between the UV seams， which I feel impossible to use some photoshop technique to fix it. I am certain that this object only uses one smoothing group. It is a game-res model, just being curious if I missed something important or there is a way to bake better normal maps.
 I have seen Glauco Longhi did the similar thing  https://www.youtube.com/watch?v=C7XsmpKvVRA

jtdx8866

In the video, from 28:40 he started talking about it