ok so i checked into this and i think it could possibly be that you're jumping to the pre_battle label instead of calling battle_start
pre_battle should only run one time at the start of the game--in the sample project it jumps there each time you select the battle option since you're not intended to keep your progress there. the pre_battle label sets the player's stats to level 1 since that's the default, which is why i assume that's what's happening!
sorry for the confusion, and i hope this helps! i can try to set it up more intuitively the next time i update this project haha