If it is intermittent then it could be a stale cache. Clear your browser cache, CDN cache, host cache.
Having said that, if you see a shortcode then it is a server side php-rendering issue (where the shortcode is parsed).
If you are using the Gutenberg editor expect flaky operation with 3rd party blocks and even some core blocks. Test comprehensively on every major release for a while...WordPress continues to make substantial changes to the core that potentially impacts any theme especially older themes.
Regarding your specific problem...
From the debugger is looks like you are using the Gutenberg editor.
If so then be aware that shortcodes are not rendered in any core block other than the Classic and Shortcode core blocks. 3rd party blocks may or may not render shortcodes.
Caveat: I have had more consistent operation of shortcodes in the core Classic block than the core Shortcodes block.
What type of block are you using?
NOTE: If you just started typing without explicitly selecting a specific block type then you are typing in a text block (which is the default block type) and shortcodes are rendered as text in a text block.
Hope that helps. Let us know.