Hi @Rene Wagner ,
According to your description, you have to do a Full Crawl operation.
This is because the Search service application administrator or site collection administrator added or changed a managed property. A full crawl of all affected content sources is required for the new or changed managed property to take effect.
For more information, please see this TechNet documentation.
Thanks,
Echo Du
===========================================
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.