The problem is the new experimental feature of Elementor Element Caching.
You can find the setting under Elementor > Settings > Features > Element Caching
If active, you can set under Performance how long Elementor caches the CSS source file before a new one is created.
The plugin does not cache the Elementor CSS source file. If Elementor creates a new CSS source file in the meantime, it can no longer be found in the frontend and display errors occur.
If you have a display error in the frontend, check the CSS source file via the browser console.
This will then generate a 404 error.
https://imgur.com/a/bYSfMm8
