[Hustle Pro] Hustle Pro popup tied to CSS ID not opening on all pages

We have set up a popup in Hustle, which is designed to open when buttons / links with the CSS ID of #free-ebook are clicked.

The popup is launched in two places – from a panel half-way down the home page (which works) and from a footer widget (Sign up for a free ebook). The footer widget works on some pages, but it does not work on the invidual book pages

e.g. https://wordpress-35220-1172637.cloudwaysapps.com/book/saxons-bane/

which use template single-book.php, or on individual blog posts e.g.

https://wordpress-35220-1172637.cloudwaysapps.com/2020/01/cover-reveal-draca-2/

which use single.php. There is nothing untoward in the browser console. I can’t work out what the difference is between places where it works, and places where it doesn’t.

Maybe you will see something we’re missing.

Thanks!