After a good few years of using Google calendars, I recently ended up switching back to Apple’s Calendar app and iCloud calendars. One thing I’ve noticed since switching (which I remember from my earlier experiences of Apple Calendars) is that while editing an event, switching a calendar can sometimes cause duplicates. It’s not the biggest issue— I just delete duplicates when I notice them— but I’m curious about the cause. Has anyone else experienced anything like this?
Is the duplication due to the Calendar app, or is it due to the iCloud calendar? On a Mac or on a mobile device?
Mobile device (iPad). I used to see this happening on my Macs as well.
App vs iCloud: I’m not altogether sure. I switched from Google Calendars to iCloud Calendars and pretty soon after switched from using Fantastical as my primary calendar app to the stock Apple Calendars app. Interestingly, I just tried to test this: created an event, closed the edit dialog. Changed the calendar. Left it for a few minutes. On returning to Calendar, a duplicate event appears— an event in the calendar it was originally in, and one in the calendar I switched it to. Opening Fantastical on the same device shows the same. However, opening on a different device only shows the event in its original calendar. Opening Calendar’s iCloud web interface shows the same: no duplicate event, but instead the older version in its original calendar. So the duplicate seems to be limited to the device on which it’s created.
Worryingly, deleting the older version deletes the version that’s synced to iCloud, meaning the updated version is now device-only and not synced. Nightmare. Turns out that this is more of an issue than I originally thought it was.
My next step is to check whether I can create duplicates in the same way via Fantastical. Either way, it’d be good to get to the bottom of this…
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Further: it’s not limited to Calendar.app. I’m able to reproduce the same issue in Fantastical. Hrrrmm.
I have seen this. Nearly always (for me) the duplicates will disappear after a while. And by a “while” I mean it might take 10 mintues or so. I suspect this is a sync issue, and Apple is erring on the side of preserving data instead of losing it. (I also see this with Fantastical, which sees my iCloud calendars.)
Very occasionally I’ve had a duplicate persist after a long period and I’ve had to manually fix things.
I’ve learned to wait a bit before assuming I need to fix something, as it usually sorts itself out and sometimes my “fixes” make it worse.
If I’m doing major surgery to my calendars, especially if I am changing the names of calendars or switching lots of events from one calendar to another, I take it offline while I’m making all of the changes. Once I’m done, I go back online and everything syncs smoothly.
I’ve also seen the same thing happen in Contacts (duplicates showing up immediately after editing, and then resolving themselves).
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This doesn’t seem as helpful as the title suggests:
… and it looks like the problem is a long-term issue (from 2015):
Life advice! I’m now imagining this as my email sig…
That’s the methodology for my currently running test. I’ve left a three test calendar events I was able to trigger duplications for in my calendar since my last post a couple of hours ago. Sad to say, the duplicates still remain, and the most recently edited copy hasn’t synced. 
Nonetheless, good to know I’m not the only one seeing this.
That tracks for me. I think it was around 2016 that I made the switch from iCal to Google. Again, good to know it’s not just me.
I think the way forward for now is a bit of behavioural engineering: pause and don’t edit a newly created event until said event has synced.
Thanks for the responses!
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I use Google Calendar and have never had this problem even when I use the Apple Calendar on Mac and IOS to access it, so the problem is likely iCloud. If so, then using the web version of Calendar on iCloud.com to monitor what is happening might be helpful in diagnosing the problem.
Time for a silly question: the calendar you move the event to, isn’t one that is only on your device is it? Just checking something that caught me out. iCloud seems to not want to delete events when I change the calendar to a local one, but I don’t use those anymore.
All of the calendars I’m working with are iCloud calendars. That said, questions (silly and otherwise) gratefully received!
Thanks for this! This is pretty much what I was doing with today’s experiments: making edits on my device then checking the web view of my calendar (along with my calendar on other devices) to compare…
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Missed that fact in your later post 
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It might also be worth trying the old “turn it off and back on again”. That’s your only option since there’s no formal way to reset the sync mechanism for iCloud.
I would try turning off iCloud calendar syncing on all of my devices, then waiting a bit. Like 30 minutes. Then turn one on, wait for data to sync, then turn the next one on, etc., until you’ve got everything turned on again. Maybe that would be enough to kick it into cleaning up its mess? It may not clean up duplicates, but it should ensure that all of your devices have the same data (including the same calendars).
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