This has happened with a few of my games that are published here. Basically it just doesn't want to read game input when it's already in use with the webpage. I even ran into a similar issue with other browser games on this website, yet it's rare. Sorry if you're unable to test out the game, but I appreciate you for trying.:)
If you're still interested in playing the demo, all I have left to say is as the game loads, just click on the game's window and/or enter in fullscreen during loading and mash the XCV keys or arrow keys to in a way "wake up" the input. Other than that, that's all the advice I know of :( Hope you have a good day:)