The game only saves each morning at the start of the day. What you describe is considered savescumming, which is not a glitch and most games can be "cheated" using this method. Items you get from diving will also be lost when resetting the game.
This is a singleplayer game, and I am a solo dev, implementing a method to completely eliminate savescumming is no easy task.
Speedrun com is responsible for what they consider acceptable in runs.