We have a 2015 C30-sport top with lots and lots of factory stainless brightwork. Only rust we've ever experienced has been underneath a few of the mounting bases which were not bedded correctly leading to trapped saltwater causing some rusting.
Fast forward to earlier last year when another vessel crashed into our transom resulting in the need to fully replace the swim platform railing... Ordered a new factory railing (originally and currently built/produced by Bolton Stainless in Canada). After installing the new railing, within two weeks it looked just like yours, and continues to develop similar rust patterns constantly (though less frequently) even after fully cleaning, polishing, and chemical passivation all while the rest of the original 2015 stainless has nothing more than a water spot or two. I suspect a lower grade of stainless than what has been advertised, or perhaps contamination from their supplier, hard to say but very frustrating to deal with now.