Appointments+ Duplicating Appointment ID

We are using Appointments+ in a production environment. Twice that we know of, the system has lost an appointment:

1. Two unrelated appointments were scheduled at the same time.
2. The system assigned both the same appointment ID
3. The system sent confirmation emails to both.
4. Only one of the appointments was stored in the DB. It appears the second appointment overwrites the first.
5. On the date of their appointment, the customer shows up and is very unhappy when there is no record of their appointment and they are not actually on the schedule.
We know the lost appointments existed because the customers forwarded their confirmation emails. In both cases we checked Appointments+ Settings > Log and found the two appointments with the same ID number. I am attaching screen caps.

In one case we know that one of the appointments was made by the customer in the front end, the other by an employee in the back-end. The other time happened two weeks ago and we're not sure exactly what happened.

Have you experienced this problem before, and do you have a fix? It has already resulted in 2 angry customers. Our admins are afraid to enter appointments in the back-end now, but they need to be able to.