Nintex Forms shows wrong entries in a selection list

Hi all, This is my first entry.

We are using the German version of Nintex Forms.

When an external login happens from an english speaking country, then the english variant of Nintex Forms is loaded. This is ok.

But the customer has entries in a list selection which do not exist in our sharepoint list. How can this be. Is there somewhere in Nintex Forms a buffer that I don't know about that can be deleted? Or is there another solution ? I am grateful for any suggestion. (I am the admin, it can't be a visual problem).

Kind regards Matthias