What if they were being lied to about the ammo? That's the first thing they themselves should check. It's the first thing we do when we have a gun that malfunctions. You try a different type of ammo. If that doesn't fix it, you try a different magazine. If that's not it, only then do you suspect parts as the problem.
Besides, Sig tests these guns with every make, type, and weight of ammo known to mankind..... Before they ever ship one. If ammo is a problem, they'll know which brand weight, and type to avoid. This all regardless of what the customer tells them. When you take your car into the dealer, they don't listen to you. They will diagnose the problem on their own, regardless of what you tell the service manager. That conversation never reaches the mechanic who ends up under your hood.