Did the screws fracture at the base of the tapered head? Typically that would be from loosing the clamp load ( not being tight, also a shear condition). Just so you know, S.S. is softer than most grade bolts and subject to fracturing. Typically S.S. is never hardened, not sure they even can. I've never been able to harden stainless. I know they would rust but if you replaced them with grade 8 screws, they would most likely never facture again. Paint the head of the screws after installing, put regular oil on the threads before installing will help stop that corrosion.
Thanks for letting guys know to check theirs!