So i removed the custom HTML and replaced it by some text and/or simpel HTML
Results is ok, meaning no broken js functionality
Pasting back the following html breaks it again:
<iframe style="border:none;width:300px; height:550px;background-color:#ffffff;" src="https://www.facebook.com/plugins/likebox.php?href=https://www.facebook.com/pages/Jeugdorkesten-Peel-en-Maas/1476933519225709&width=300&height=550&colorscheme=light&show_faces=true&stream=true&header=false" title="Facebook">