At the current moment, Google Calendar syncing issues are known to affect all users that are using Google Calendar and we have not yet released a fix.
For now, we suggest disconnecting and reconnecting Google Calendar from Nimble in Settings >> Networks & Imports and then your Google Calendar should sync. If your calendar goes out of sync, please repeat these steps.
We have found that disconnecting and reconnecting Google Calendar once a day in the mornings will give the best syncing throughout the day.
We plan to fix this issue in Q2 of 2013 because the scope of the project is large and we are currently focused on other areas of improvement.
We sincerely apologize about any inconveniences this may cause in the meantime.
If you have any questions, please email us at email@example.com.