Strongest Level 1

The raid failed. In a desperate situation, facing the dungeon boss's self-destruction, Lee Geonwoo is left alone in the boss room due to a teammate's betrayal. Just when he thought everything was over, he coincidentally obtained a dagger. Afterwards, his life completely changes... He managed to save his life, but his hard-earned level returned to 1.
-'Mosquito' has been caught.
-Level has increased.
It's clear that the level has increased, but why does the level remain the same?