[Question] What are some good examples of gaming that is hard to detect?

https://www.lesswrong.com/posts/Qiqc7qoavfC6DFoh4/what-are-some-good-examples-of-gaming-that-is-hard-to-detect

For example, an RL agent that learns a policy that looks good to humans but isn’t. Adversarial examples that only fool a neural nets wouldn’t count.