It seems that there is an issue with the mcustomscrollbar "scrollTo" function not working in Chrome, although it works fine in FireFox. No errors are showing up in the console, so it appears to be a browser-specific problem. I even tested the functionality on this page and encountered the same issue with vertical scrolling only in Chrome.
$('body.Office .use-custom-scrollbar').useCustomScrollbar();
var scrollToElement = $('.day.today').length ? $('.day.today') : $('.day.future:first');
scrollToElement = scrollToElement.length ? scrollToElement.closest(".one-day-container") : $(".one-day-container:last");
setTimeout(function () {
$('body.Office .use-custom-scrollbar').mCustomScrollbar("scrollTo", scrollToElement);
}, 0);