RollingLinkedList inherits the interface from LinkedList, which explicitly implents it. All subclasses of Serializable classes are Serializable.I don't understand what you're suggesting. RollingLinkedList doesn't implement Serializable, does it? And I know I didn't change JDKs. Can you show me exactly what you think happened.
You said you "only checked it against OpenJDK 15", is that the jdk you use for everything? For some reason I was under the impression that you used a "newer" jdk to check this.
But JDK version is just one of a myriad of things that can make a build generate a different serialVersionUID. It's possible java is free to just ... generate a different one *whenever*. I am not even sure if it must be generated during compile time at the latest, or if can depend on runtime environment ...