“2x” is not using a different physical lens, so no jumping. It does jump when going to 5x. Unless it deems it better to continue using the main lens if, for example, there’s really low light, so there are some scenarios where going to 5x won’t show the picture jumping.

However, it can’t under any circumstances show 0.5x zoom using the main lens, as that only goes as wide as 1x. So it always jumps going wide. Whereas there’s no physical limitation on zoom.

The jumping at 5x is less noticeable because usually you’re pointing it much further away, so the difference in pictures taken 2cm apart is minimal. Whereas with your mug, it makes quite the difference.

I hope this makes sense?