tab CPT twice

Hello,

A gd_place post has predefined tabs such as map, rewiews, etc. Visiting settings of a new CPT e.g. gd_publication I linked gd_publication to gd_place using the link field and now whenever I access a gd_place post it shows me an additional tab “Publication” as defined. So far so good as this is normal behavior and intended. But what certainly is not normal that all linked posts which are shown under said tab are shown twice i.e. repeated (e.g. gd_publication 1, 2, 3 and then again gd_publication 1, 2, 3). When I check gd_publication (also in the db) there are no duplicates. It really just repeats the full set of the same posts. Any idea what it could be? What should I look at? Could there be an issue with post 2 post /your list plugin (even though deactivating the two did not change anything)?

Thank you