I thought I checked everything, but clearly I missed that one. That's the only link that doesn't work. What you would find in Game.gd is missing parentheses on line 17, so the solution to the first puzzle is 17. The folder that is inaccessible due to the bug doesn't contain anything else you need to progress in the game.
Thank you for being patient with me. I hope that with this information you can progress in the game and report any other errors that you find.