Probably your actual seams.
Your textures have to be perfect for it to work. Normals and roughness included.
Dcc have higher precision than the engine (by a lot in all aspects of rendering).
You may need to increase the quality of the UVs either by making the UVs right (match up on the edge of a pixel so that the image is always perfect), or by changing the setting on the mesh.
Same with your actual mesh.
Smoothing groups have to be right, with hard edges where needed.
The issue on the shirt could be a rogue flat face or 2.
Overall, the mesh also has settings for lighting that you need to tweak. A lot. To get the shadows to play nice.