Don't want treatments (services) within one appointment to be split among different staff members? You can configure this as follows:
Go to Settings
Click on Calendar in the settings panel
Go to the Advanced calendar settings
In the bottom left, choose Free Moment Finder
At the bottom, enable the option: "Only one staff member per client for an online appointment"
Click on Save online booking
Go to the Basic calendar settings
Disable the option: "Assign a preferred staff member per treatment in online booking"
Click Save at the bottom
ATTENTION
Make sure that the knowledge is properly configured for each employee!