Can’t link existing posts

I have posts/pages in 2 languages (English, French), which have all become disconnected.

I am trying to re-connect posts in the Events post type (The Events Calendar) manually but when I start typing a post title, it’s not appearing in the drop-down suggestions so I am unable to connect them.

Has this happened to anybody else? I am not sure how to solve this problem without having to recreate the pages over again.

Thanks in advance!