Appointment not showing in email and getting doublebooked

Hi,
One of my client is having trouble with overbooked appointments. When books the appointment the slot does not show up in email, only the surrounding text.

Also on the Booking Orders page, I find booking “without” an appointment. It says “Appontment: ” then empty space, then customer details.

Those bookings experiencing this, are not actually booked, and this creates trouble with overbooking.

Any help appreciated. Thanks!