There's no use to add loop to the lowpoly, it's just gonna add up to ur final tris budget. Can you show the highpoly without subdivided? I wanted to see your loop placement. I'm thinking to add more loops on here, this is just guessing though cus I'm not sure how you place your control loops.
Hmm..you put the support loop on the highpoly and it makes it look even worst? that kinda strange.. Can you show how the highpoly base looks like with wire (no turbosmooth)?
Sure. As I said, if I add one more loop to the low poly the issue is duplicated. That means the high poly is not the problem. In fact I baked the same meshes in other programs and this only happens in Painter.
Happened to me before, it's your highpoly surface that didn't perfectly flat. Try what Jerc suggested, add some support loops but for your highpoly mesh. You can check your highpoly by assign a high gloss material on Max (seems like you're using Max?) and switch the viewport display to Faceted, can you see the differences…