Buggy scrollbar
The scrollbar on the site has a lot of bugs. It's because it does not use the native scrollbar, but a library. I think function is more important than look in this case.

Personally in my projects I use only css to enhance the look of the scrollbar. I suggest you do the same. When all browsers support it, you just need to make minor css changes.

https://css-tricks.com/the-current-state-of-styling-scrollbars/