Customer not showing up in group booking after submission

Over the past week, we have had customers who booked an appointment with us, but we are not receiving notification of a new booking, and their information does not appear on the booking calendar. The customer is getting the confirmation and reminders; they also appear in the customers' list, but when we select the event on the calendar to view who is attending, they are not listed. It only affects some people who sign up. 

We also recently noticed that someone canceled, but we have not received that notification. Again, it does not affect every customer who cancels, as we have received cancellations before and after this incident.