Elementor loads custom fonts through @font-face rules that reference files in wp-content/uploads/elementor/custom-fonts. When the URL points to a missing file, the browser returns 404 and falls back to a system font.
Browser blocks the request if CORS headers are absent, if the page uses HTTPS and the font URL uses HTTP, or if server headers prevent the font MIME type. Optimization plugins that rewrite CSS often change the URL, producing the same result.