I've got the Gcal <-> Appointments+ two way sync working otherwise, but there seems to be a problem with available times and current events in Gcal.
If my service provider has set a long appointment (eg. 3hours) manually to his own calendar, that period of time shows correctly as unavailable in appointments+ before the event. But when the starting time of that specific event passes, the whole time period is suddenly available in appointments and customers can make double bookings towards the end of that long appointment.
I have the latest version of the plugin and wp.