Accordion doesn’t stay open

As soon as I open an accordion it immediately closes again. Also, I only can open each item only once.

Console says:

accordion-custom.js?ver=5.4.13:31 Uncaught TypeError: Cannot read properties of undefined (reading ‘end’)
at callback (accordion-custom.js?ver=5.4.13:31:83)

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