How to collapse the Table of Contents lists

Hello,

I added a Table of Contents widget in Elementor editing page. All of the displayed Table of Contents are collapsed, when I click the webpage. I mean the Table of Contents only display the header “Table of Contents”.

Only one Table of Contents on one webpage does not work, and it is https://guardianchem.com/articles/degreasing-oil-sands-equipment/ When I open this webpage, the Table of Contents collapses with all the lists.

Could anyone kindly give some tips to resolve this problem?

Thanks in advance!

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