When you get the message “Please note that you are switching to WordPress default editor" then you are on a Gutenberg page switching to a classic page. When you do that WordPress will convert your page content and the results may be unpredictable if Elementor is in the mix.
Up until WP5.0 the old style editor was in use. This is now referred to as the “classic” editor. Since WP5.0 WordPress has two editors for you to choose from…the “classic” editor and the new “Gutenberg” editor.
Elementor blocks were originally designed to be used in the “classic” editor. For backward compatibility the “Gutenberg” editor offers a “classic block” and a “classic shortcode block” for legacy shortcodes.
So to run a Elementor block on a “Gutenberg” page you would put it into a Gutenberg “classic block” or “classic shortcode block”.
To confuse things further Elementor has releases some native Gutenberg blocks.
So I don’t know whose block you are using…Elementor’s classic shortcode block in a Gutenberg classic block or a Gutenberg block or an Elementor Gutenberg block!
And if you switch your page between classic and Gutenberg, WordPress will convert all the content. Normally that yields accurate results but I would not count on that in this case since Elementor is a page builder.
My recommendation if you want to use Elementor is to disable Gutenberg site-wide then try again using a “classic” site. Your site is a messy soup right now. Or, as an alternative, make your site Gutenberg and drop Elementor. Your choice.