Elementor tries to create a critical CSS file for each page. The file lives in the uploads folder and is referenced by the front‑end HTML. When the process stops, Elementor shows a red notice in the editor.
The stop happens because the system cannot write or retrieve the CSS file. Reasons include missing write permission, a setting that forces external files on a read‑only host, or a conflict that removes the file before Elementor reads it. Heavy PHP usage or a syntax error in custom CSS also aborts the generation.
When the file is absent, the page loads without the intended styles. Layout breaks, fonts revert to defaults, and speed tools report missing critical CSS. The error appears in the console as 404 or 403 for the CSS URL.