In June 22nd, 2021, a programming bug in Lichess' Puzzle Storm and Puzzle Racer games caused some players to achieve excessively high scores that are otherwise beyond their abilities. See e.g. this recording of the bug by Joseph Leung.
The Lichess developers could have decided to delete all Puzzle scores from June 22nd and to recalculate the data sets based on them. But presumably for performance reasons, they only recalculate these data sets when