Many auth plugins define the ability to lock user profile fields by calling print_auth_lock_options() from their config pages. This only defines a set of config settings called field_lock_xxxx

However, if the plugin is defined as external, moodle will try to call update_user_record_by_id() in moodlelib.php to update the user from the external auth service. About halfway through it attempts to access a config property of the plugin called field_update_local_xxxx (for each field read). These fields don't exist in the plugin's config and will throw a notice.

The only plugin that defines these is LDAP and it does its own processing. This section appears redundant (and throws notices).