Active only fires on second click?

Question

JavaScript

Why on the last element in the navigation, adding the active class works the second time?
Of course, I suspect that this is due to the fact that I still have onscroll handlers, but I can’t find an error, it’s not an option to find an error at all, as for me. If you remove the onscroll handler, then everything works, but then I will lose the feature that the client asks for, when scrolling to each skekia, the class in the navigation changes to the menu that is currently scrolled. Help someone who cares. https://jsfiddle.net/f1y8ezL2/3/