That said the writing has been on the wall since Java 9's project Jigsaw. If you have a product that depends on it, I'm surprised you were caught unaware. With more control over what is exported, the amount of compiler optimisations possible greatly increases.
> To balance the need for integrity with both the circumstantial, convenience uses of JDK internals and the essential uses, Java gives the user – the application's owner (typically its author, maintainer, or deployer) – the final say on which strong encapsulation boundaries are in place and which should be ignored. This freedom is offered under the guiding principle that the ability of one component to encroach on the boundaries of another must be explicitly granted by the application. Libraries cannot choose to obtain encapsulation-busting "superpowers" without the knowledge and consent of the application's owner.
The point made in the article is that it's often third-party libraries that do this, breaking invariants in your code. And, with older JVMs, it won't be immediately obvious to you as a user of that library that this is happening.