The smoothscroll.js code is largely broken and is preventing us from shipping scroll top interop. With the scroll top interop behavior activated sites fail to scroll at all with the wheel event. This library was corrected a few years ago but the web continues to clone the broken version and we have been blocked in shipping this long implemented fix for interop. Smooth scroll has been enabled in Chrome for a number of releases so using custom smooth scrolling is not necessary anymore.
Docs: https://docs.google.com/document/d/1yMAUU0wCeP7BIlQujqfwe3LBnG0QJaqymbkZwor9u60/edit#