Appointments+ booked slots not showing as booked,

I'm in the testing phase of a site and am trying to get Appointments+ working. I'm running into trouble where I book appointments and they auto-confirm as confirmed, but then the booked times aren't blocked out on the calendar.

Per the thread here, I'm using the following shortcode to display the calendar(s) for this specific service:

[app_monthly_schedule service="4"][app_pagination][app_schedule service="4" class="twentyfourhour" logged="Click on an orange time slot to reserve equipment."][app_confirmation]

I have it set in the backend to auto-confirm all appointments. I have "use built-in cache" set to No. I'm getting the confirmation/notification emails with the correct booked times. BUT, if you book an appointment on the calendar above, then go back to the calendar, it doesn't show as booked.

I've tried waiting for a while (24 hours after making an appointment) and this problem persists.

Ideas? Thanks,
Michelle