On the experimental servers (also experienced this on stable), if I lean and scope in while also holding breath and crouching then you get knocked out of breath really fast.
You specifically get out of breath and start swaying as if you had lost all breath. It basically goes from 0 to 100, unlike when you regularly get out of breath when scoped in.
This happens every time i attempt this with either the winchester or the b95 with a hunting scoped mounted.