Hello,
First of all I'm sorry for the bug and for the (very) late answer. I saw your message ( <3 ) and thank you for your extensive help in finding the issue.
I was VR-less for the two previous months and not able to check the final export runs of the game (and it was fine in the Godot Editor). I found my (very stupid) case-sensitive mistake and...
The bug you mentioned is now fixed !
Let me know if you manage to finish the game, you still have almost 40% to do :p
(About the bonus level, it was feasible, you had to push the joystick when jumping to reach the platform. It felt very counter intuitive so I also changed this specific level)
Hope you can enjoy it with your son :)
PS: I also added keys for redeeming the game on Steam