There are several reasons why the Google Calendar sync may not work. The two most common are 1: inactivity in your account, or 2: The 2-way sync was not started. FOr either of those scenarios, the fix is the same. Simple go to your Profile page, make sure the Calendar sync tab is set to “on”. If it is already on, then turn it off and on again. Turning it off and on is the way to activate the 2-way sync.