Hi Xanmal!
What OS and webbrowser are you using and when does this error show up?
I have checked the SharedArrayBuffer checkbox on upload and just tested to play the game on Edge, Fire Fox and Chrome with no issue (on Win10).
I don't know if there is anything else I can do, have you tried an other browser or emptying the cache/hard reload for the website?
Best regards.
// WinZenT