Pending appointment automatically removed without me doing anything

I have set up and am testing Appointments+ in preparation for a site launch in a few days.

Yesterday, my client successfully set up an appointment. I then received the automatically-generated email that notified me that an appointment required confirmation. When I clicked on the link in that email, the appointment was there and waiting. That was all fine and I was ready to get my client to test the process of confirming the appointment. But before I could do that, I found that this appointment (and others I was creating) were later being automatically given a "removed" status in the system.

I have granted site access. The appointment has an id of 5 and I keep changing its status to pending and after a few minutes its status changes to removed and it is no longer listed in the Pending appointments list and is instead in the Removed appointments list.