Your 3D model’s normal map seams in Substance usually stem from poorly aligned UV islands or inconsistent baking settings. UVs with too little gutter space between islands or unmerged split edges (for hard surfaces) cause texture mismatches. Baking issues like a misaligned cage (used to project details) or too-tight offset let neighboring island details bleed, creating visible lines.
To fix this, increase the UV gutter to 2-4 pixels, merge overlapping islands, and adjust the baking cage to sit slightly outside the model—this stops detail bleeding and reduces seams.