I tried out Polylang and after disabling it, all my categories are gone from the WP Admin Categories and Tags windows. They are still in the WP_terms table in database as well as attached to posts - posts already tagged / categorized still have the tags / categories in frontend and the archive pages for them work as they are intended to.
I can't add any new categories - they disappear as well.
Reinstalling polylang did not fix the problem
What could be the reason why the categories and tags don't show up in WP Admin and how could I fix it?