Calendar Syncing Issues :: MacBookPro M1 Chip, Sonoma to iPhone SE 2nd Gen, iOS 17.1.1

It continues to amaze me that Apple, a $3 Trillion market value company, can't solve calendar and address book sync between Mac OS & iPhone & iPad issues. For me the address book sync has not worked for years. Now I am experiencing similar calendar event sync problems between Mac OS & iPhone.

Apple built that big "ring" headquarters in California; but their software product quality began to suffer long before that was built and the software quality continues to decline. Apple customers are the ones that suffer from the poor quality; but, apparently, the corporation will not suffer, until customers move to some other software products.

Oh my!

Macbook Pro M2, OS 13.5.2 and iPhone 13 - latest software whatever that is.

I had this problem several months ago and called Apple - the tech had me replace files from a recent Time Machine back up and I have avoided syncing again until this week when - yes, indeed, the multiple calendar entries reappeared. I phoned Apple again and once again she walked me through a restore of my computer's calendar from a month-old backup, but that was ok. Both techs said they had never seen this before when I shared my screen. The second said that the solution was to update the MacBook to Sonoma, but I have been hesitant to do that without knowing what else might break. Now I read here that that is NOT the solution. I

I have also noticed some corruption in calendars on the iPhone - all day events that come from downloaded info - US Holidays, for example have multiple entries there.

The good news for me was I was able to capture the missing calendar data on my computer from my iPhone, so that part of the sync worked - just had to reenter it on the computer.

Occasionally, I must transfer playlists from my computer to my phone. My process going forward to do this will be to back up my computer through Time Machine, sync my phone and then restore my computer calendar from the back up. I will need to figure out the restore process so I don't have to phone Apple. This really is not acceptable, but there it is. I don't want to use iCloud.

Glad that I found this thread - I don't feel so alone. If anyone discovers that Apple has actually fixed the problem. please post that so I can update and stop living in fear of connecting my phone to my computer.

Thanks you all for posting all of this!

I sync via wifi or USB/lightning cable (not iCloud). After upgrading my MBA M2 to Sonoma and my iPad (5th gen) to ios 17.1.1 (happened around the same time), I cannot get the respective calendars to stop screwing each other up.

First, all my MacBook Air's calendars disappeared on the upgrade to Sonoma.

Syncing with the iPad caused me to get calendars back, but with multiples of all-day events (multiple entries on a given day OR yearly repeats becoming daily repeats). I got more than 900 repetitions of a few past appointments. The iPad's calendars were turning single-day all-day events into two-day events, all starting one day earlier. Not only would events change repeat rates, some changed sub-calendars. I've set both devices to the same date and time zone to try to deal with the two-day birthday problem. But the problem still happens. I changed the iPad's doubled events to single-day events, and the MBA ended up with doubled events.

At one point I trashed my Mac's calendar files and replaced them with my last Monterey back-up. I got both the iPad and MBA calendars the way I want them.

Then I sync'd them again after adding a new appointment to one of the devices, and everything messed up again.

Both before and after replacing the MBA's calendars, subscription holidays and birthdays would become either (a) two-day events repeating yearly on both devices, or (b) single-day events repeating daily on the MBA, or (c) two-day events repeating one after the other on the MBA. Or the birthdays would disappear altogether.

Other appointments disappeared altogether, especially some more than three months in the future. I tick the box for not syncing anything older than 90 days, so does the program then not sync anything more than 90 days in the future???

I wonder what will happen if change all the events' subcalendars to "Calendar".

Well, here's what I've figured out. All the all-day "events" (many of which I used as reminders) were now starting a day earlier. So in both the computer and the iPad, one-day events became two-day events, four-day events became five-day events, etc. Furthermore, anything that repeated yearly (such as birthdays) now repeated daily. Everyone's birthday was a two-day event in both the iPad and computer, but starting every day of the year -- for both devices. No matter how many times I changed the repetitions back to annual, and the start and finish dates to the proper day, the events kept reverting. Also, appointments more than 3 months in the future variously got duplicated or eliminated altogether on both machines.

First: I eliminated all the birthday events I had created so that all birthdays came via Contacts. But I had to create new contacts in Contacts for many birthdays just using people's first names and the birthdate. For example, if a Contact entry was for, say, Pat and Leslie Lee, the only way to get separate birthdays was to have a Pat contact page and a Leslie contact page. So there's a Contact page for their numbers and address, but separate ones for first names and birthdays.

Next: In the Macbook Air, I deleted all the multiples. Then I created a calendar called Calendar, and merged all my regular sub-calendars into it (i.e. eliminating all the sub-calendars). For the iPad, in order to get rid of all the multiples I restored a back-up from this past spring. Then I added a calendar called Calendar, went back as far as there were events, and changed each sub-calendar to Calendar, and then I deleted all the other sub-calendars. Syncing still was changing all single all-day events in the iPad to two-day events and annual events to daily events. And multiples were still showing up in the Mac after syncing.

Then: In the iPad, I reduced the syncing to 45 days back, then I deleted all regularly repeating events, and anything designated an all-day event. In the Macbook Air, I corrected all-day events, and then I deleted then re-entered all regularly repeating appointments. Syncing put the all-day events back into the iPad, where everything became one day longer, starting the day before the correct date. But things didn't change in the Mac. Who knows why! Maybe because I wasn't adding the iPad's screwed up all-day events back into the Mac. I deleted the all-day events in the iPad.

Next step(s): I re-created my sub-calendars one by one, adding each in both the Mac and the iPad and syncing after each addition. I made some corrections in each (especially the iPad), and eliminated the all-day events in the iPad again (every time). I did this again for each addition of a re-created sub-calendar.

Because I hadn't backed up any of these iPad iterations, I was limited in which calendars I could officially sync. So sometimes I had to sync "all", even though there were officially four of them, two of which I had to un-tick in both machines (anything associated with my e-mail address, for example, because that definitely recreated some unending repetitions). Once I had all the sub-calendars back and had fixed all-day events and eliminated duplications, I ejected and turned off the iPad, re-started the Mac, and reconnected the iPad using the USB cable (wifi makes syncing too slow). I wanted to back up the iPad with the calendars as they were. The cable was already plugged into the iPad, so I then plugged the cable into the Mac. I mention this because it turned out to be significant.

I then had rather an ordeal trying to stop the iPad from automatically syncing when I plugged the cable into the computer. The problem was that I didn't want the music or audiobooks to sync until I'd made sure I could sync the calendars without incident. After a few bouts of this (stopping the sync, waiting and waiting for it to stop, ejecting, reconnecting, etc), I disconnected the cable from the iPad, plugged it into the Mac, then plugged the cable into the iPad. That time, the syncing did not start automatically. So I backed up the iPad to the Mac. Then I synced again. Now all my sub-calendars are listed for syncing, and I can choose which sub-calendars to sync.

The iPad still adds an extra day to past all-day events, but they're not affecting the Mac's calendars now. But that may be because I'm deleting them in the iPad whenever they show up.

After all this, it seems to me that the only way to avoid these problems is to stop using the all-day setting. This is definitely not satisfactory, but it's all I can figure out for now. The other thing I need to do, it seems to me, is to make sure that I sync events further back than 90 days in order not to lose appointments booked more than 90 days in the future.

By the way, I haven't been able to sync contacts for years and years. I don't even try anymore. I just enter new contacts separately into each of my devices.

Oh, how I miss my Palm Pilot....... :-(

I had an epiphany yesterday. I found that the calendars in previous years still had a lot of duplicates. Since my plan is to backup my MacBook Pro with Time Machine, update my iPhone and then restore my calendar, I wasn't happy. But THEN I realized that almost all of the existing duplicates were events that I had set for repeating yearly. When I looked at one, I found that the "Repeat Yearly" setting had been switched to "Repeat Daily." To fix this, all I had to do was search for the event ... lots of entries.... go to the first entry and change daily to yearly. I was asked if I wanted to change only that entry or all and selected "all", all of the dups disappeared. I repeated this for each dup - there were things like birthdays, annual bill reminders, etc. But now it is all cleaned up. When I sync my iPhone next time, I will try turning off calendars as part of the sync and just manually enter new dates as needed. This does not take Apple off the hook for creating and not fixing the problem, but I think it will make my life easier.

Experiments in adding all-day calendar events (repeating and non-repeating) to Mac, to see how they show up on the iPad:

I have tried turning on just "time zone override" (an iPad setting), just "time zone support" (a Mac Calendar setting) and turning on both at the same time. I invariably end up with the iPad starting the all-day events a day early (but ending them on the correct date).

Syncing a second time: if I make no change on the iPad calendar, syncing does not make any changes to the events in the Mac's calendar. If I have deleted the events on the iPad, they'll be deleted on the Macbook Air. So that remains normal.

Experiments in adding all-day events to the iPad calendar: I added a few all-day events on the iPad, some non-repeating and a couple repeating (1 event weekly, and 1 monthly) and then synced with the Macbook Air. It messed up the Mac's calendar. The single-day, non-repeating all-day events were fine. But weekly and monthly all-day events all became daily events on the Mac.

The conclusions: (1) Add single all-day events to the Calendar only via iPad; (2) Don't add any repeating all-day events to either calendar.

It's not the ios that's the problem. My iPhone can't go beyond ios 16.x.x, and all-day events misbehave the exact same way. It's not time zones, because I can create events starting at 00:00 one day and ending at 00:00 the next, and they show up on the one designated day. It's Sonoma and the "all-day" thing that's the problem.

just checking in to say i have an m1 14inch macbook, iphone se3, and am having all the same problems with calendar sync.

i too am a heavy user of all day events, and have many repeating events.

i've tried all the solutions shown above and gotten zero results.

seems that if icloud was removed from the picture and we reverted to the 'old days' everything would be hunky-dory.

thanks for update. i'm still not using icloud, but i'm not using the sync either, i'm double entering in both calendars.

as it happens i had a problem with notes these past few weeks which i'd been working with a senior advisor on until resolved. i had pointed out to her (it was a her) this specific discussion and sent a link to it which she has recieved. i pointed out that the odds that 2 people running exactly the same hardware encountering exactly the same problem at exactly the same time i.e. after the 'upgrade' to sonoma were even larger than those of winning the powerball, and thus there was a definite problem at apple's end.

i personally think, and pointed out that all of the icloud centered apps have problems (notes, reminders, calendars, contacts, messages) of one sort or another which weren't present previously, and that although it seems sonoma is the enabler, the possibility that the rush to get osx to run ios apps coupled with the new m1-m3 processors coupled with the push to get everyone to use icloud hasn't been flushed out to be as bullet proof as some of the old nuggets like snow leopard etc.

oh well, maybe there will be a dot release that eventually corrects the non-existant problem.

Syncs are not multiplying or deleting appointments anymore, but all-day events (however long they are) are still adding an extra day in the iPad.