Android calendar nightmare...

A recent strange incident with my Android calendar synchronization almost drove me insane.

It appears to be a very popular issue that has many causes and solutions.




Here is my 2 cents with a solution that worked for me...

First, the symptoms of my situation:

Calendar sync stopped working, everything else still gets sync'ed

- The calendar stopped synchronizing any new entry and just showed the cached existing items up to a recent date.

- Any new item added on the phone would not be saved. Any new item added from a PC would not be sync'ed into the phone.

- "Calendar" had disappeared from the Sync list in the Android settings, all the other apps were still listed and working. 

- There was no calendar listed under my account in the Calendar settings

- Trying to add a calendar would bring a prompt for Sign-in a New or Existing Account which would consistently fail with the "couldn't sign in" error.

My working resolution (root needed):

- Removed the calendar.apk from system/app folder

- Restarted the phone

- In Settings>Accounts> Google>account name> Removed the account using the menu and added it again

- From Play, located the Calendar app from Google and installed it.

From this moment, the Calendar should be back in the Sync list

- (Optional but recommended) moved the new com.google.android.calendar.apk from /data/app to /system/app and restarted the phone.  This turns the new Calendar into a system app.

Remark:

This replaces the stock/AOSP calendar.apk with the much bigger (20MB vs 2.6MB) but nicer one from the Play Store. In my case, this was a necessary part of the solution because, doing the same procedure as above with this stock apk did not help at all.

One problem, many possible causes and solutions:

I can only speculate on the causes as this happened after no obvious configuration change or application installation. I suspect the stock calendar.apk (4.4.4-1227136) in my official Android 4.4.4 from THL to have some kind of bug.

Other people have resolved a similar problem by either updating/re-installing Google Play service, 

clearing the cache and data for Google Play Framework, disabling the 2-step authentication (not used in my case), removing the Google account and re-adding it, replacing the Calendar Sync Adapter apk, ...