Duplicate birthdays in Calendar but only on Mac I have my birthdays stored in my contacts. As of late I see duplicate entries for each birthday in my Calendar on the Mac. On my iOS devices they only show up once. When I deactivate my contacts account (macOS Server account) the birthdays are removed from my calendar as expected. When I reactivate the contacts account the birthdays re-appear but only once. After a few hours Calendar on my Mac will then show them twice again. If I try to manually delete one of the events I get the error message: "You can't add or change events in the Birthdays calendar". 

Is there a why for me to reset my "birthdays Calendar" on my Mac? What else can I do? 

I am using the Sierra 10.12.2 and Calendar version 9.0

Thanks for any advice.
macOS Catalina (10.15.7)
Unchecking and renabling birthdays on the calendars sidebar will only toggle visibility and did not remove the duplicates, but unchecking and renabling 'Show birthday calendar' in the calendars settings seems to reload it - that's what worked for me.