Try to change browser or download the game. I always do that if I encounter some kind of problems.
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Yeah I do the same thing, as mentioned I tried brower and windows build already but wasn't getting anywhere.
Good news though, I tried again today and managed to get it working, even in the browser! I think I must have been pressing the wrong key to start. Becuase it is working consistently today.
Going from pressing 'space' to start on the first screen to pressing 'c' to start on the second screen was the issue it seems. And you can crash the game if you try to press 'quit' when in the browser.
Anyway I can play it now :)