Hi! As of 0.7.4, your mastery is decided by completing a quest in the End of Time, which is given when you first arrive in the end of time, rather than by investing 25 points.
Since you’re on an older character, you should talk to Gaspar in the End of Time again. It’s worth noting that if you had picked a mastery class before 0.7.4, you won’t be able to pick again. You can check which class you are by looking at the character sheet ( C ).