Google calendar doesn't sync completely

I came across this thread while researching the same issue for a client of mine. Her symptoms seem to have been triggered after the Mac had a period of inability to connect to the Google server which resulted in the Calendar app giving some error messages. After that the Mac (10.13.3) has worst symptoms of non-sync to server, but iPhone (11.2.6) is also intermittently failing to sync or taking a very long time.

Non-syncing is one symptom but worryingly there are also symptoms of entered events disappearing.

My belief is that the underlying sync engine (potentially on both the Mac & iPhone) is then getting tangled with one or several corrupted calendar entries. I don't have any proven resolution as yet but am proceeding down the track of exporting all calendar items, then completely clearing the devices & Google account of all calendar entries & then re-importing.

Temporary work around for my client is to use web browser interface to Google calendar on her Mac and the Google Calendar app on her iPhone.

I'd be happy to hear from anybody else who has a definitive solution.

I had very similar problems after restoring a complete iPhone backup to a new iPhone (replacement). Google cal dates weren't synched any more. The different calendars didn't even show up any more within the iOS calendar app when tapping on "calendars" (option in the center of the calendar app bottom for selecting calendars to be shown). After doing almost everything I found in the web, saying: checking account enabled/disabled toggle states for calendar, completely removing and re-adding Google account in Settings -> Accounts, enabling two-factor-authentication on Google side, checking the famous "sync setting page" of Google and so on...

... there was one last thing that helped me, it's like back in the good old days:

Did you try a reboot? – No. – Do it!

Yes, it's true: An iPhone-/iOS-Reboot helped me. After waiting a couple of seconds, all calendars and dates showed up again.

*sigh*

See some articles Share your calendar with someone - Calendar Help

See Google Calendar events on Apple Calendar - Computer - Calendar Help

Fix sync problems with the Google Calendar app - Android - Calendar Help

To configure , apple calendar with google services the user must have an Apple ID created see this article Sign in with your Apple ID - Apple Support

And must set up iCloud account iCloud: Set up iCloud

See this article Access iCloud, Google, and other calendars in Calendar on Mac - Apple Support

If you keep calendars in Internet accounts—for example, iCloud, Exchange, Google, Facebook, Yahoo, or AOL—you can use the accounts in Calendar on your Mac, and access all your calendars and events in one place.

Thanks for the heads up. What seems to be working for my client at the moment is to use different "calendars" within the same Google account. We deleted & re-added the account to her Mac and the re-sync for the original calendar *seems* to be working there, but still not working on her iPhone.

Frustrating to not know the real underlying reason so as to know what work around has best chance of being stable.

Note: Her original/default calendar in the Google account that I exported to an ics file then had to be manually edited down to 11 smaller files before the Google web interface would allow re-upload.... which I tested on an empty account but we didn't end up doing for my client.

I had this problem for weeks. But, today, 25th, March, 2018, I found this had been fixed without any setting changed.

I can see my iCal with google calendar synced in my desktop Macintosh again.