Today we made an update of the difficulty after 400+ day
Previously, the progress of songs in the top was too fast. We slowed it down, because at the late stage of the game it was unreasonably difficult to get into the top.
After the update, new songs that will appear will be of lower quality. So the old save works, but you will fully feel the update either in 3 months after downloading or if playing from scratch.
But I think 3 months is still much better than playing with such difficulty as it was)