I've identified a few changes in the code which can lead to unexpected errors.
Missing from Person.js
set address(addr){ this._address = addr; }
Person.js param order changed from:
class Person { constructor(ssn,firstname, lastname, birthYear = null, address = null) {
To:
class Person { constructor(firstname, lastname, ssn){
Student.js param order changed from:
class Student extends Person { constructor(ssn, firstname, lastname, school, birthYear = null, address = null) {
To:
class Student extends Person { constructor(firstname, lastname, ssn, school) {