Hi, it's due to missing permisions for getting the font file:

Access to Font at 'https://3dselfie.wereldprint.nl/wp-content/plugins/easy-appointments/components/bootstrap/fonts/glyphicons-halflings-regular.woff2' from origin 'https://3dselfie-shop.nl' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'https://3dselfie-shop.nl' is therefore not allowed access.

You must set it, or embed those fonts inside your theme. Best regards, Nikola