Images not showing on frontend

Hi,

We have the slider installed a year ago, and it did work a few months. But now we have this problem: Images are loaded, but not showing until you click on a button. But then they disappear suddenly.

This is the page where we added the slider: https://tanderij.goot4u.nl/informatie-over-de-praktijk/impressie-praktijk/

https://www.ads-software.com/plugins/easy-wp-parallax-slider/