All due to the fact that a level 400something apparently didn't know you can hear Sombra as she stealths up and was doing it right around the corner from me. Knew she was likely coming from the backside of the final point on Blizzard World, so I turreted up on the bench near the small health as Bastion and waited.

Went down pretty fast almost immediately afterwards. XD

TL/DR: Remember, Sombra isn't a ninja before she's fully invisible. And even then there's a blink period where you're still visible immediately after engaging the stealth.