Calendar events disappear
I have been using several calendars on my Mac. After a Security Update of the OS (with reboot) I had to newly log in to iCloud. I left the checkbox 'Sync Calendar to iCloud' checked (although I did not use iCloud so far. I got a message something like 'Moving calendar events to iCloud' with a progress bar. When syncing had finished all calendar events were gone, I just see the names of my calendars but not a single event.
How can I restore those items? I have a recently sync'd iPhone, but apparently events shown there are not transferred to my Mac.
Hans
MacBook Pro 15", macOS 10.12