Media translations not linking

I’m trying to translate all our existing media, because we need localized ALT tags for SEO. We haven’t had the polylang media translation activated from the start so we need to update all the existing media.

I followed all the steps in https://polylang.pro/doc/working-with-media/ but when I update an existing media file with our default language and afterward try to add the other translation they don’t get linked like they do in posts & pages. It just creates a new separate media object in the other language – although I clicked the + Button. They never get linked!

Any ideas?

https://www.ads-software.com/plugins/polylang/