Hi Bugsbane,
Thank you for your response. Because of my network setup it was needed to do several tests and the outcome is that it must be a local issue like my adblocker because nico had the same issue -> https://help.nextcloud.com/t/chrome-problem-with-sharing-contacts/1834
Unfortunately I can not confirm the resolution because today I am able to share my contacts and calendar again without NC or network changes and so I can not find out the main cause 
Best regards
NC2016