It’s more likey the export.
Import the fbx into blender and check.
Thing is. A weight of .01 will cause issues but will not be directly visible.
However posing the mesh in Blender would reveal such a vertex by causing the jacket to offset.
Go into pose mode, move the hands by rotating the clavicle all the way up.
If you see distortion happening that’s it.
If you don’t. Can’t possibly be the paint.
Assuming this doesn’t happen in iclone because it is somehow happening during export.
Not sure how possible that is.
It’s more like than the import adding stuff.
The standard import for meshes will ignore weights below .001
And triangulate for you.
That’s about all it does which can be considered “special” though… afaik.