Appointments+ Not Sending Notifications Properly

Appointments+ has stopped sending notifications properly. I first noticed that I was no longer receiving admin notifications. I checked my settings, and the option to send confirmation emails is checked off; I'm also listed as admin of the site in the General WP settings page.

I checked the A+ log and I don't see entries for admin notifications listed. It appears clients and providers, however, are getting their messages.

In addition, as part of my trouble-shooting, I made an appointment in incognito mode in Chrome, and the log doesn't show any emails being sent (to client, provider, or admin), and I didn't receive any email.

I know that my University's email isn't blocking messages from the site, because I am getting notifications when an appointment is cancelled.

Any ideas what might be happening?