The problem I think is that when you define an invariant, you are also defining an infinite number of "implicit" invariants. And it's hard to know a priori which of those implicit invariants is not an actual invariant over time.

Take a simple User type

  type User {
    name: string
    email: string
  }

This describes some obvious invariants - that a User will have a name and an email.

But it's also describing some less obvious invariants, e.g. that a User will not have a phone number. This has implications if a phone number ever does get added to a User type, and your system has to deal with two different versions of Users.

(This isn't just an academic problem - the problem of trying to evolve fields over time is the reason why Protobufs got rid of the idea of a "required" field.)

And this is an example of a very simple implicit invariant. In practice, systems that interact with each other will give rise to emergent behaviour that one might think is always true, but is not guaranteed.