Scratching my head over this and hoping peeps can help. I am projecting a Perlin Noise texture to a cup. If I use a triplanar projection these odd lines and artifacts appear that are clearly inline with the wireframe (see images 1 & 2). The same texture using UV projection works fine (see image 3). In fact, blurring the triplanar also fixes the issue (see image 4) but then this obviously causes some issues at the UV seams. In image 5 you can faintly see that the wireframe lines are actually appearing in the triplanar projected texture.
To my knowledge, the bake is fine, the smoothing groups are fine. The issue isn't just within Substance, the lines export within the normal map and appear in Marmoset.