I had a problem with renaming slugs - once I renamed a slug, the old version remained and then I had to do manual redirects, so as to avoid duplicate content.
This is what Webflow support advised me to do:
"when the page is deleted or renamed, the original pages not yet been unpublished. The solution would be to unpublish the site, then remove the pages or rename them, and then republish the site.When the site pages are deleted and not unpublished first, then the pages get stuck in CDN cache."
I didn't know about that and I'd like to suggest that a warning tooltip appears upon renaming slugs, hinting you to unpublish your site first.