If a user group is assigned any of the sn_hr_core roles, that group cannot be edited by someone who can normally edit the group.

Application administration is enabled for Human Resources Core(sn_hr_core) application, so the users should have 'sn_hr_core.admin' role to assign other users any of the sn_hr_core roles and edit the user groups which are assigned any of the sn_hr_core roles.

Review the documentation related to Application administration.