Hi!
The plugin only changes the search query – what posts should be displayed,
but does not changes the default search page layout.
The default search output with products (default search query) displays on this page https://www.babybow.eu/?s=toy&post_type=product (without search_id parameter). And it returns empty page with title ‘Page not found’ but with status 200.
You could try to deactivate my plugin and refresh page https://www.babybow.eu/?s=toy&post_type=product. If nothing changes and it will be still empty page then problem may be in the theme, I think in the child theme. Probably there is a ‘search.php’ file presents and it overrides parent theme ‘search.php’ file.