The player that you open with http://localhost:3000 is cached on your browser. Whenever you start a game with this player, your local app will keep that information. To play again there are multiple things you can do:
Click on the Reset current session button in the bottom right menu to reset this player, and create a new game for this player to join.
Click on the New Player button in the bottom right menu to open a new tab with a different player (you will see tab with an id).
The app will automatically ("hot") reload when save changes to the code.