It appears to be a designer bug, related to the migration to localization support.
Webflow support suggested a workaround which is to replace your linked item with an HTML embed, and then use the Add Field to manually create the URL with your slug.
I’m using a work-around by including a Page URL field for each item in the CMS, and copy pasting the URL without en within it. And when specifying the link settings, instead of collection page, i just use URL and reference it to the field within my CMS collection
So—are we to assume that it’s still not safe to update any site with CMS links because it will break the site and damage its SEO? Any ETA on this bug finally being fixed so we can update our CMS sites @Emily_Lonetto ?!
I don’t recall even seeing a formal acknowledgement of this by the team, other than support replies. Basically be careful about publishing. If this bug makes an appearance on your site, triage it with the redirects and the script, and double-check your canonicals in case the script needs to be extended for that.