I've noticed that whenever you reach one of the mastery levels after having cooked the dish on an easy appliance, you do not get the notification that you've reached the mastery level. You still get the rewards though, I think. I've noticed my gems went up about the time I should have earned one, but with my coin totals and XP being much larger numbers and changing all the time, I have not noticed if I get the coins and XP I'm supposed to.