There are currently two different ways to interactively snap viewport to aligned axes, both with very poor usability:
1, The older viewport snap, which is activated by first holding down the middle mouse button, and then pressing the alt key.
2, The newer viewport snap, which is activated by first holding down the alt key, and then holding down the middle mouse button.
1, is not usable because it does not correctly switch between perspective and orthographic viewport mode when the view is snapped. More on that here: Viewport orbit snap still does not work with Auto Perspective
2, is not usable because it’s extremely unpredictable. It requires stopping and thinking before you can predict which view you end up when you perform it, and if you perform it from perspective, non aligned view, you will end up in a pretty random direction.
So instead of fixing the auto perspective bug in the first one, the second one was implemented in a lot worse and more counter intuitive manner.
What is even worse is that now they both live side by side.
And what is EVEN WORSE is that they both occupy the same hotkey combination, just in different order.
This solution is way below the usability standards of Blender 2.8 and something really needs to be done about it. At the very least, the new viewport snap should be removed. It’s truly terrible.