Thank you for your comment! Sorry if it wasn't clear enough, we don't know why Unity made changes in the scene after building the project, but you could navigate to other levels if you go to the edges of the scene and then click "E" standing over any edge :] (It was also supposed you could also choose your skin in the middle platform, but we couldn't achieve it correctly).
Top right edge - level 4, Top left edge - level 5, Bottom right edge - level 2, Bottom left edge - level 3