Set up a pufferfish player detector by getting a pufferfish in a minecart, in 2 blocks of water pushing it into a pressure plate on a fence post for alignment (the cart should end up halfway between a top slab and the pressure plate; the slab being necessary to stop the fence from connecting to it). When a player is near, the fish puffs up to trigger the plate, then shrinks when they leave and the plate turns off. But if you unload the world and reload it, when it loads in, the pressure plate will be pressed as though the fish's hitbox is puffed up even though the PuffState is 0. If the fish's puff is triggered again and then it returns to its state 0, it will turn off the pressure plate ("resetting" the hit box, I think).

The hitbox should be based on the puff state, so when the world loads and it's in PuffState 0, it should have a small hitbox from the start, rather than needing to be puffed up and deflated again to reset that.