The business rule that adds the customer role to a contact has been read-only. Due to which an admin cannot change the BR according to business requirements. This caused an issue when the Contact entities had customized role assignments or processes built around them.
Now, the business rule is changed to be -
If the customers wish not to have the default behavior of role assignments for the Contact, they can deactivate this business rule all together.
Open business rule 'Add customer role to contacts'
Verify that it is not editable as it was set to read only
Upgrade to Fixed In versions or get the business rule deactivated by raising a Case to ServiceNow Customer Support.