If you're using buttons, swiping shouldn't do anything. I suspect you're closing the app by incidentally tapping the Home or Back buttons while you're swiping up.
If you want to close an app while using 3 button nav, then just tap the Home button (or Back enough times to back out of the app).
Various animation speeds can also be adjusted or turned off completely in Developer Options as well. That's the first place I go when I get a new phone.Try turning off animations in accessibility settings. I turn them off anyways because it makes your phone feel a whole lot more responsive.
That (animation) did it. Thanks Very much.