I’ve had the same issue and I’ve found it seems to be because the editor mode (available to any browsers logged in to the project on webflow) requires third party cookies to display an ‘edit site’ button at the bottom of the page.
Tested: You will note that the white space is not visible if you visit your site in incognito or any browser not logged in to webflow.
Quick fix: Allow third party cookies for your site in the site settings on your browser.
Full fix: Recommend adding a cookies dialogue so users who are logged in to the webflow project can accept third party cookies without having to change settings themselves in the browser.