There is a major business flaw in the Round Robin Calendar.
Currently, if a contact is assigned to a user, the round robin will do a round robin to all the users and will not book the appointment to the assigned user. It will round-robin the appointment and not change the assigned user.
What happens here is if there's a salesperson (user) assigned to a contact. When the contact goes to the Round Robin Calendar, they can be scheduled with another salesperson (user).
There needs to be an option in the Round Robin Calendar that if a contact is already assigned to the user, then schedule the appointment with the assigned user.