Try repairing your Google Calendar.
(To Repair Google Calendar in eM Client).
Click the Calendar icon at the bottom left of eM Client.
Then “Right click” your “Gmail Calendar” and “Click Properties” at the bottom
Next click the “Repair” tab at the top and finally click “Repair”. This will take time as eM Client has to rebuild the local calendar cache etc
Next if still the same problem, then could be you might need eM Client updating. You can check for the latest versions via the following webpage.