If you are using the multilingual plugin WPML and you set up the language settings to use custom folders with the language code in it, e.g. yourdomain.com/en/ you may run into an issue where opening a page resulted in an error 404. This is especially when the staging sites permalinks are disabled.
To fix that you can switch the WPML language settings on your WP Staging staging site to URL based language like yourdomain.com/lang=en?