When you complete all easy level track, then medium unlocks. Then you complete some tracks of medium, close the game and open again. But now current track is set to the last track of easy level, not the track of medium which you played last time. AND: all previously completed tracks of medium is LOCKED, except the first track of medium.
When you complete all easy level track, then medium unlocks. Then you complete some tracks of medium, close the game and open again. But now current track is set to the last track of easy level, not the track of medium which you played last time. AND: all previously completed tracks of medium is LOCKED, except the first track of medium.