Well, its not an L Grade thats for sure.
I think Dave is on to something with perhaps too much time in the bath, or some other control issue.
Giovanni is right 2mm for a pickling bath is extreme.
Yes, it is 304 stainless steel, although, as js55 pointed out, the carbon content is somewhat high for an L grade.
In any case, this is not the reason for a corrosion of 2 mm.
I'd say that the reasons explained by Dave Boyer should be further investigated.
By the way, and this has nothing to do with corrosion. When I was a child, many and many years ago, there was a famous movie star called Charles Boyer. Anything in common?
Giovanni S. Crisi