I’m not sure what is the reason now. it can be in your data or some bug in the Org Chart. Let us find out.
Please confirm that you use SharePoint user profiles as a data source, not SharePoint list.
Could you open developer tools of your browser, navigate to the “Console” tab, clear Org Chart cache, refresh the page and reproduce the issue?
Then send us a screenshot of the “console” tab and of the web part.
Additionally, please navigate to regular SharePoint people search and try to search the same employee by the same keyword “birne”. People search usually is available at the right top corner of a page:
If SharePoint people search is configured Org Chart uses it internally. So, the issue with people search can be also a reason.