Increasing friction of time between playing newest unplayed levels & resuming older unplayed levels
As someone who has clocked in around 3 months worth of levels (assume a month is 30 days: 90 days x 3 difficulty levels = 180 levels!): a notable flaw in this game is that when a day has passed, and a new level has been opened up, when you finish a level in one of the three difficulties (casual, normal, and challenging), the game seems to assume that I beat that level (disregarding not completing the two other difficulty levels) and moves the avatar cursor back to the next currently unbeaten level.
The problem multiplies in the amount of days or months I have to scroll back just to beat the other two difficulty levels after beating the first time. Imagine someone with 12 months worth of levels beaten, when a new level comes up after a day has passed, and is beaten in any difficulty, if the person want wants to beat the other two difficulty levels of that day, they must scroll a lot twice in order to beat that day with all difficulty levels covered.
Perhaps this is intended for players who just want to clear only one difficulty level per day and not finishing up the two other difficulties, but this design decision makes it increasingly tedious for those who want to clear levels in all difficulties.
The optimal way to satisfy both types of players (players who only beat levels by one type of difficulty, and players who want to beat levels on all three difficulties) is an toggle option on the sensitivity of level clearing (move the avatar cursor ahead after a level is beaten in one difficulty, or all three difficulties). Perhaps cover type of players who beat two difficulty levels per day.