Adding a querystring breaks Insert Pages

Hi there, I’m using Insert Pages with a custom post type and a custom template. It works great, but when I pass any query string value (examples ‘foo=bar’, ‘width=5’, ‘direction=horizontal’) via the Custom Querystring field, the preview in the Gutenburg editor displays

Block rendered as empty.

If I go ahead and publish the page, the page is inserted correctly and the querystring is passed through to the template. It’s just in the editor where things fail.

Can you give me some guidance? I’m new to WordPress in general so I may be overlooking something obvious.