This version isn’t 100% rolled out yet. Once it is, this will become available (shortly after the “Maintenance break” notification)
I can only assume this is like the other seasons, where the missions are triggered once you reach the specific levels with the task/appropriate enemies. Keep playing and I’m sure they will show up.
Not sure. Perhaps contact SGG and Google Play.
Who will probably both do nothing but point fingers at each other and after hours of needless “support” the problem will correct itself.