Calendar sync’ing between iMac and iPhone via iTunes and USB cable has stopped working

So after 2.5 weeks of having no relevant responses whatsoever and one that did not even address my question, I finally figured it out myself.

One of the .plist files for the calendar application had somehow become corrupted. By removing the .plist files (there were two or three of them), then starting the application and letting them rebuild the situation has been resolved. Note that I still had to go through all of my CONTACTS. For some reason after the calendar .plist files were regenerated, a bunch of duplicate information showed up in several contacts (e.g., the phone number repeated 7 times, etc.)

I'm putting this information here because I searched for hours trying to get an answer to this question and there was just nothing out there! Every question out there on the web was usually dealing with contacts, and in most cases they were all involving sync'ing via iCloud. I don't think I was able to find any questions at all like mine, and I spent hours looking. I hope this info helps somebody.

I added a new event to a calendar on my iPhone, connected it to my iMac and ran the sync. Here is the trace from the Sync Logfile. There is supposed to be a 5th process named "iCalExternalSync" that is supposed to run to transfer the updated/new calendar events between the iMac and the iPhone. This process that always used to run when a calendar update was needed is no longer running at all! The last time it did was back around February 13th of this year. Why has this thing stopped running?

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2020-04-24 23:44:19:376|AppleMobileDeviceHelper|48915|0x7f97dd506c20|ISyncManager|Warning| Sync Server was - Active Last Time

2020-04-24 23:44:19:397|SyncServer|48916|0x7fc1bb506850|Logging|Info| Logging initialized, engine version 726 : log level 3

2020-04-24 23:45:10:946|AppleMobileSync|48921|0x7fa84040e320|ISyncManager|Warning| Sync Server was - Active Last Time

2020-04-24 23:45:10:949|AppleMobileSync|48921|0x7fa84040e320|ISyncManager|Warning| Could not retrieve ISyncClient with id com.apple.Keychain!

2020-04-24 23:45:11:027|AddressBookSync|48922|0x7f9ec7410c80|ISyncManager|Warning| Sync Server was - Active Last Time

2020-04-24 23:45:11:177|AddressBookSync|48922|0x7f9ec7410c80|Stats|Stats| com.apple.AddressBook: fast sync com.apple.contacts.CalendarURI, com.apple.contacts.Contact, com.apple.contacts.Date, com.apple.contacts.Email Address, com.apple.contacts.Group, com.apple.contacts.IM, com.apple.contacts.ImageTransformationInfo, com.apple.contacts.Phone Number, com.apple.contacts.Related Name, com.apple.contacts.SmartGroup, com.apple.contacts.Street Address, com.apple.contacts.URL

2020-04-24 23:45:11:236|AppleMobileSync|48921|0x7fa84040e320|Stats|Stats| com.apple.MobileSync.2401e788669ad1da9771747347ac238e72a23d69: fast sync com.apple.contacts.Contact, com.apple.contacts.Date, com.apple.contacts.Email Address, com.apple.contacts.Group, com.apple.contacts.IM, com.apple.contacts.Phone Number, com.apple.contacts.Related Name, com.apple.contacts.Street Address, com.apple.contacts.URL

2020-04-24 23:45:11:371|AppleMobileSync|48921|0x7fa84040e320|ISyncManager|Warning| Could not retrieve ISyncClient with id com.apple.Keychain!

2020-04-24 23:45:11:504|AppleMobileSync|48921|0x7fa84040e320|Stats|Stats| com.apple.MobileSync.2401e788669ad1da9771747347ac238e72a23d69: fast sync com.apple.calendars.Attendee, com.apple.calendars.AudioAlarm, com.apple.calendars.Calendar, com.apple.calendars.CalendarOrder, com.apple.calendars.DisplayAlarm, com.apple.calendars.Event, com.apple.calendars.Organizer, com.apple.calendars.Recurrence

2020-04-24 23:47:18:691|SyncServer|48916|0x7fc1bb506850|Server|Info| Cancelling all sync plans.

2020-04-24 23:47:18:692|SyncServer|48916|0x7fc1bb506850|Server|Info| Goodnight, Gracie.

chris_g1

You said: "I understand you're running into an issue syncing contacts between your Mac and iPhone using iTune". You obviously didn't read my question which is about Calendars and NOT Contacts!

This response does not help at all. It only talks about how to normally sync calendars and totally bypasses my question. I have been manually syncing my calendars and contacts over usb via iTunes for some 15 years now. I know how to do all of that. It has recently stopped working though. As you can see in my original note I am using the most up to date iOS, itunes and a reasonably recent macOS.

Furthermore, ALL of it was working only a few weeks back! Something has become corrupted in my calendars somehow.

Note, My contacts are continuing to sync just fine. But if I add a new event to a calendar in either my iPhone or my iMac and then initiate a sync, that new event will not transfer to the other product.

So again, does anyone have a clue as to what is going on here?

Has this question now been dropped? I had a nearly instant response to my original post but this one has been setting here for 5 days now