There are only a few options. I'm only familiar with the 320 by looking at pics. The first thing that is evident is a fairly complex striker assembly. For any striker weapon to fail, it has to be a broken/bent trigger engagement surface, a bent/sloped striker catch, or a combination.I’m definitely stumped. The internal safeguards on all striker fired pistols are of such a simple and basic ingenious design, I just can’t wrap my head around it and where or how that even a design flaw could by pass 3 separate internal safeguards?
The Sig mechanism has more components and therefore more potential for tolerance stacking, but I am still always suspicious of improper handling, first and foremost. It may seem harsh, but IMO if you cannot prove you didn't do it- you did it.