I explained why that won’t work in your other thread but to recap you have put the sticky nav inside an element called #page which basically only contains the stickynav. Therefore the nav is only sticky within that element and as soon as that element scrolls away (which is immediately) the sticky nav is no longer sticky.
You need to either remove the element called #page or indeed wrap #page around the whole page content and then the nav will stay sticky while the rest of the content in #page scrolls.
A sticky element is only sticky in relation to its immediate parent so when you want it to be sticky in relation to the body element it needs to be a direct child of the body.