There are certain difficulty cycles generally applied in Royal Match. This occurs roughly every 10 levels and changes in a loop as each area is unlocked. I will provide a more detailed explanation below.
Starting from level 50, every level ending in 5 becomes a HARD level, and every level ending in 9 becomes a SUPER HARD level. In the cycle of every 10 levels, the first level starts as easy and gradually becomes harder until reaching the hard level. The first level after the hard level is relatively easy. Then, the tension starts increasing again up to the super hard level.
In addition to these mini-loops, I believe there is also a more general cycle in place. It involves a gradual increase in difficulty until a new area is unlocked or until BONUS levels are reached. When a new area is unlocked, it introduces new obstacles for players to adapt to, providing them with a period to acclimate while lowering the tension and allowing users to progress. As the player approaches the Bonus Level or as they near completion of the tasks within the area, the game's tension increases, and it becomes progressively more challenging.
During these moments of increased difficulty, user motivation is actually quite high. This helps to keep players engaged and less likely to give up easily. The high motivation stems from being on the verge of unlocking a new area and the curiosity about the new obstacles, which keeps the user motivated.