"Reuse an existing field" - list contains only field_comment

Hi!

I have a weird problem: If I want to add an existing field to a node bundle (/admin/structure/types/manage/bundleName/fields/add-field), I can only chose field_comments, no other field is shown, regardless how many I've created before. It's not the same for paragraph entity - there, the list contains all existing fields.

What are the steps to find the cause for that?

Thanks!