With a factory gun in proper working condition and a proper firm grip, it's a combination of two factors for the ammo.
115 gr. range ammo is cheap, it's low power for lower recoil, and doesn't have as much quality checks as premium self defense ammo. The fact that it's lower power also means it has a smaller margin of error of what will cycle a semi auto.
All factory ammo will have enough power/velocity to cycle any functioning properly semi auto, unless otherwise stated, when loaded inside manufacturing specs. It's the few that slip through without the specified amount of powder, that may fail. And the lower the powder charge, the higher the probability of it failing to properly operate the slide.
Also more care and quality checks are put into defensive ammo for obvious reasons.