Rank Math “forgets” set meta description for custom content type

Hi, we have a custom theme on our page, which proves an additional content type (“publications”). Rank Math generally speaking works correctly with that, except for one issue. While loading the page editor, Rank Math doesn’t recognize the meta description that is already set.
What I mean is: when I open the page editor, Rank Math shows an error that the focus keyword was not found in SEO Meta Description and in the preview, above the “edit snippet” button there is no description. When I go to edit snippet, each field is filled, but next to description shows 0 length – see screenshot https://imgur.com/a/E981Ta7
It’s only when I make any change in the description (e.g. add a space), that Rank Math figures out that there is something then and recognizes there is a keyword in the description etc. However when I go to update the page and the editor reloads, the same happens. Still, the description is being saved – I think the issue is only with the preview. It doesn’t happen for other post types (the default ones).