Submenus stopped working

Sometime in the last few weeks, I noticed the sites submenus are not displaying properly.

If you look on the left menu, Kewanna Town Info has an arrow next to it, indicating that there is a submenu, but hovering over it reveals no submenu.

On further inspection, it appears to be caused by an outdated JS plugin Superfish. The version on the theme is from 2008, and is version 1.4.8, while the latest version is 1.7.10
https://superfish.joelbirch.design/

the errors in Chrome on the Console page are these:

superfish.js?ver=5.5.3:64 Uncaught TypeError: Cannot read property 'msie' of undefined
    at HTMLUListElement.<anonymous> (superfish.js?ver=5.5.3:64)
    at Function.each (jquery.js?ver=1.12.4-wp:2)
    at n.fn.init.each (jquery.js?ver=1.12.4-wp:2)
    at n.fn.init.$.fn.superfish (superfish.js?ver=5.5.3:62)
    at HTMLDocument.<anonymous> (superfish-init.js?ver=5.5.3:3)
    at i (jquery.js?ver=1.12.4-wp:2)
    at Object.fireWith [as resolveWith] (jquery.js?ver=1.12.4-wp:2)
    at Function.ready (jquery.js?ver=1.12.4-wp:2)
    at HTMLDocument.J (jquery.js?ver=1.12.4-wp:2)
(anonymous) @ superfish.js?ver=5.5.3:64
each @ jquery.js?ver=1.12.4-wp:2
each @ jquery.js?ver=1.12.4-wp:2
$.fn.superfish @ superfish.js?ver=5.5.3:62
(anonymous) @ superfish-init.js?ver=5.5.3:3
i @ jquery.js?ver=1.12.4-wp:2
fireWith @ jquery.js?ver=1.12.4-wp:2
ready @ jquery.js?ver=1.12.4-wp:2
J @ jquery.js?ver=1.12.4-wp:2

superfish.js?ver=5.5.3:35 Uncaught TypeError: Cannot read property 'serial' of undefined
    at getMenu (superfish.js?ver=5.5.3:35)
    at HTMLLIElement.over (superfish.js?ver=5.5.3:20)
    at I (hoverIntent.min.js?ver=1.8.1:2)
    at hoverIntent.min.js?ver=1.8.1:2
getMenu @ superfish.js?ver=5.5.3:35
over @ superfish.js?ver=5.5.3:20
I @ hoverIntent.min.js?ver=1.8.1:2
(anonymous) @ hoverIntent.min.js?ver=1.8.1:2
setTimeout (async)
I @ hoverIntent.min.js?ver=1.8.1:2
(anonymous) @ hoverIntent.min.js?ver=1.8.1:2
setTimeout (async)
I @ hoverIntent.min.js?ver=1.8.1:2
(anonymous) @ hoverIntent.min.js?ver=1.8.1:2
setTimeout (async)
I @ hoverIntent.min.js?ver=1.8.1:2
(anonymous) @ hoverIntent.min.js?ver=1.8.1:2
setTimeout (async)
h @ hoverIntent.min.js?ver=1.8.1:2
handle @ jquery.js?ver=1.12.4-wp:3
dispatch @ jquery.js?ver=1.12.4-wp:3
r.handle @ jquery.js?ver=1.12.4-wp:3

superfish.js?ver=5.5.3:35 Uncaught TypeError: Cannot read property 'serial' of undefined
    at getMenu (superfish.js?ver=5.5.3:35)
    at HTMLLIElement.out (superfish.js?ver=5.5.3:25)
    at hoverIntent.min.js?ver=1.8.1:2
    at hoverIntent.min.js?ver=1.8.1:2

The page I need help with: [log in to see the link]