JS error in WP store locator

Hi, I checked with WP Store Locator and was informed that there’s a JS error in the theme, which probably breaks the WP store locator plugin.

navigation.js?ver=5.4.1:172 Uncaught TypeError: Cannot read property ‘offsetWidth’ of null
at HTMLDocument.<anonymous> (navigation.js?ver=5.4.1:172)
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)

Would you let me know how to fix it? thanks.

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