This isMogified('password') is not function

The problem might be related to the fact that you're using ES6 arrow syntax instead of a plain function as the callback. ES6 arrow functions change the semantics of the this keyword, which might affect how mongoose handles the callback internally.
http://stackoverflow.com/questions/36794709/inside-schema-method-scopes-this-is-empty-in-mongoose-4-4-12