Does it only happen in the Windows version, and the HTML5 version connects successfully (can be tested in About > Server Data)?
If only in the Windows version, does running
curl --http1.1 -I https://graphomata.com/game/
(pre-installed on Windows 10+) produces "HTTP/1.1 200 OK" as the first line?
If also on the browser, what relevant errors do you get in the Developer Tools (Console and Network tabs)?