If the appointment selection is locked, it only means that another user is making an appointment within the same area; you cannot make an appointment until that specific appointment selection lock has cleared. This is one of the Core Practice features to avoid any double bookings for the same time slot.
Below shows an example of when an appointment section is locked. This indicates that another user is booking/clicking on the same roll of appointment section. To unlock this appointment section, simply ask the other user (you can see who is using that time slot) to click away from the appointment book and it will automatically revert back to normal.
If you have any other questions or concerns, please do not hesitate to click on the yellow HELP button for further assistance. We'll be more than happy to assist you!