The X-Frame-Options response header tells browsers whether a page may be displayed inside an iframe. When the header value is DENY the browser blocks any framing attempt, regardless of origin.
Elementor renders the page preview inside an iframe that shares the same domain as the editor. The browser requires the header to be SAMEORIGIN or to be absent. A DENY value stops the iframe from loading, leaving the preview area blank.
Typical sources of a DENY header include server configuration files, security plugins that enforce click‑jacking protection, and WordPress core hooks that add the header for admin screens. Any of these can override Elementor’s need for SAMEORIGIN.