This is probably coming from whatever is setting your script loading to async (maybe a different plugin that you have installed to perform some sort of optimization). Basically Photonic’s JS is not getting executed on your site. Your photos are all present, but Photonic performs a step at the end once all photos are loaded – it makes the photos visible. Try disabling the plugin that is setting the async attribute on Photonic’s scripts. Currently you have this showing up:
<script nomodule async='async' src='https://www.lgomorika.be/wp-content/plugins/photonic/include/js/front-end/nomodule/combo-slider/photonic-baguettebox.min.js?ver=20210413-64848'></script>
<script type='module' async='async' src='https://www.lgomorika.be/wp-content/plugins/photonic/include/js/front-end/module/combo-slider/photonic-baguettebox.min.js?ver=20210413-64848'></script>
I believe if you are able to get that async='async' removed, things will work.
