If you have SEO links activated in the tenant and changed SP Pagebuilder to production mode, you could randomly get wrong URLs when hovering over a page item in SP Pagebuilder. You could see the page in front-end but not be able to edit it.

Work-a-round is to copy the content and graphics from front-end or export the page item from the Db and then re-create a complete new page and trash the page that is returning the 404.