It's possible you need to learn attunement first. Every 10 levels you can learn attunement which allows you to learn a new magic style. For instance, I'm a wind mage but if I want to branch to water or nether, I will need to learn attunement first. However, I'm just a player, not the dev. Cryswar might have more info for you!
I remember in early versions the attunement were traits, but now I think they are granted automatically when you complete the training for the elements. Regardless thank you for pointing that out, I checked the game and I do have attuned with neather magic but still the spells don't show up. Also I never seen anyone with the same problem so hopefully it's not a major bug.