enroll/database/cli/sync.php crashes with a fatal PHP error when adding users to a course from external enrollments when the course is using groups.

PHP Fatal error: Call top undefined function groups_add_member() in enroll/meta/locallib.php at line 166

Adding require_once("{$CFG_>dirroot}/group/lib.php"); to the top of that function block (protected static function sync-with_parent_course() on line 81 of enrol/meta/locallib.php) fixes this.