Unsolved Problems in Machine Learning

I am actually not even aware of any machine learning (ML) problem that is considered to have been solved recently or in the past. This tells you a lot about how hard things really are in ML. Of course, if you read media outlets, it may seem like researchers are sweeping the floor clean with deep learning (DL), solving ML problems one after the other leaving no stones unturned. In reality, they are not, researchers actually attack relatively simpler problems in the hope of collectively solving the bigger problems, that is just how research works. You can see DeepMind aim is to "solve intelligence and make the world a better place" but they are busy building game playing algorithms.