Hi @Bernd_Eichhorn1,
So we can better assist you, please provide a brief description of your current setup using this link as a guide.
Make sure to describe your network configuration/topology, including any networking hardware currently in use, so we can have a clear understanding of how your devices are communicating.
When you selected the Core, did you select the same Core you were previously using?
Can you share a screenshot of Settings > General?