That's wierd, I tried on multiple devices and it worked on each one, have you tried reloading the web page?
If that still doesn't work, then try the gdgames version
https://gd.games/crli14/platformachine
I tried reloading it and it didn't work. Coming back later didn't help either. Neither does going fullscreen. Here's a screenshot of where it gets stuck:
I'm on Chrome if that helps... Also, same thing is happening for me on gdgames :\
