Simple SS 304 can be attacked by wet Salt. But SS 304L will be a better choice giving some higher can thickness margin. If the Quality system stipulates it has to pass the test you can not help. But the point is how outside surface is passing the test? Pl. check by simple water soak test whether your inside surface is having any iron particle contaminations ? Now, sugar being a carbohydrate it is not supposed to contain any iron or chlorine so there is no risk of chlorine attack as also the container should be hermatically sealed to prevent from any moisture. So I am not sure why this test is reqd. regards

A copper sulfate test (per ASTM A967, etc.) will quickly tell you if there is iron on the surface. Soaking it in hot distilled water for a few hours will induce rust if there is iron. It may have become contaminated as the brushed finish was applied, did you use equipment that has seen contact with carbon steel? You probably need to passivate your containers.