I'm having issues with "double bookings" with a multi-service, single-provider setup

I have appointments+ setup for a single-provider that has nearly 50 services that they provide (it's a day spa). I have two way synchronization setup with their Google Calendar, as they manually add appointments to their Google Calendar.

By default all appointments that are manually inserted in their Google Calendar show up in Appointments+ as "30 Minute Massage", which is also the first service in the service list.

I'm having an issue of double bookings. Even though they put an appointment in on their Google Calendar, a client is not able to book a "30 Minute Massage" on the site, but if the client chooses another service, such as "60 Minute Massage", every availability is open.

How do I fix this? I have one service provider providing all of these services and appointments are starting to overlap!

To see what I mean, you can visit here: http://lavishinsequim.com/schedule-an-appointment/

TIA!