It’s hard to say what could be the cause exactly, other than what is explicitly stated in the error message: You are trying to access the document object of the enclosing window of the game. This goes against the a browsers security restrictions. Either this is something you are doing explicitly or it’s something your game engine is doing.
You can also try using our CDN with modified headers, which may enable certain game engines to use functionality to improve their performance. You can learn more here: https://itch.io/t/2025776/experimental-sharedarraybuffer-support