To place it briefly:
No matter how I've bound my keybindings for my wired Xbox One controller on my PC game client, my aim down sights is triggering the 'fire' function. So far I've only been able to test this with the MP-113 Shotgun and no other weapon, but I understand that this impacts the ability to use a firearm with a controller and I'm hoping that not everyone is experiencing this same issue.
// No ammunition was required to test. Firing happening with or without ammo (clicking respectively for the lack of ammo) while aiming the shotgun.
I didn't get to see what ammo I had used beforehand, and I didn't get to test if the ammo possibly triggered the bug. The first attempt I had at aiming the shotgun was when it was loaded. So there is always a possibility that the ammunition had something to do with it, though I doubt it since after I unloaded onto a few zombies and ran out of ammo, the issue persisted.