The calendar on the Galaxy S5 keeps syncing and may not show all of the events on your calendar. This issue can be resolved by restarting the android phone in Safe Mode and then turning off Safe Mode:
1. Shut down the phone: hold the power button and then tap Power off.
2. Power on the phone and, as soon as you see "Samsung", hold the down-volume button until you see your Home or Lock screen.
3. Unlock your phone and turn off Safe Mode.