I am assuming you know mechanism of pitting corrosion as well as composition and role of elements in typical stainless steel (SS)

It eats up passive layer, so to say.

Chromium oxychlorides are not that adherent, but when you contact chromium oxide with them, such oxychlorides do form.

Perhaps lower charge of anions mean less easily perturbed by diffusion, or prefer to remain in solution than become deposited, so this layer cannot prevent electrical circuit of corrosion much

And due to mechanism of pitting or crevice corrosion, under the pits and crevices, the conecntration of chlorides (and HCl) would increase manifold), so chromium would get dissolved.

To prevent this happening requires not-so-rective metals that form insoluble chorides or chloride complexes that are incoluble and electrically less conducting themselves, like molybdenum (it has something to do with transition metal chemistry and valency, I guess), so Mo-laden SS are chloride corrosion resistant.

These Chloride ions disrupt the integrity of the passive layer and penetrate the passive layer, leading to localized breakdown and the initiation of pitting corrosion.

Stainless steel forms a thin, protective passive layer of chromium oxide (Cr2O3) on its surface when exposed to oxygen. This passive layer acts as a barrier, preventing further oxidation and corrosion of the underlying metal. So Chloride attack breaks the passive layer and leads to pitting or crevice corrosion, to prevent this using an SS with high Cr, Mo, and Ni can improve resistance to Chloride-induced corrosion, by applying a protective coating.